xref: /netbsd/external/ibm-public/postfix/dist/proto/postconf.proto (revision 6550d01e)

# This is the input file for automatically generating the postconf(5)
# manual page, the summaries of parameters in on-line manual pages,
# and for the postconf.5.html hyperlinked document.
#
# The following tools operate on information from this file:
#
# xpostconf
#     Extracts specific parameter definitions from this file, or
#     produces a sorted version of all the information in this
#     document.
#
# postconf2html
#     Adds parameter name +default headers. The result can be embedded
#     into the postconf.5.html hyperlinked document.
#
# postconf2man
#     Converts this file into something that can be embedded into
#     the postconf(5) UNIX-style manual page.  This tool knows only
#     a limited subset of HTML as described below.
#
# postconf2src
#    Converts this file result into something that can be embedded
#    into Postfix source code files.
#
# The subset of HTML that you can use is limited by the postconf2man
# tool:
#
#   * Supported HTML elements are: blockquote, ul, li, dl, dt, dd,
#     p, pre, b, i, h, and the escapes for < <= >= >. Sorry, no
#     tables.
#
#   * HTML elements must be specified in lower case.
#
#   * Lists cannot be nested.
#
#   * The postconf2man tool leaves unrecognized HTML in place as a
#     reminder that it is not supported.
#
#   * Text between <!-- and --> is stripped out. The <!-- and -->
#     must appear on separate lines.
#
#   * Blank lines are special for postconf2man: it replaces them by
#     a "new paragraph" command. Don't put any blank lines inside
#     <blockquote> text. Instead, put those blank lines between
#     </blockquote> and <blockquote>.
#
#   * Text after a blank line must start with an HTML element.
#
#   Also:
#
#   * All <dt> and <dd>text must be closed with </dt> and </dd>.
#
#   * Use <blockquote><pre>..</pre></blockquote> for examples
#     between narrative text, instead of indenting examples by hand.
#
#   * Use <pre>..</pre> for the "Examples:" section at the end
#     of a parameter description.
#
# The postlink tool automatically inserts hyperlinks for the following,
# so you must not hyperlink that information yourself:
#
#   * Postfix manual pages
#   * URLs
#   * RFCs
#   * Postfix configuration parameters
#   * Postfix README files
#   * Address classes and other terminology.
#
# The xpostconf and postconf2html tools expect the file format described
# in the comments below.  The description includes the transformation
# that is done by the postconf2html tool.
#
#   * The format of this file is blocks of text separated by one or
#     more empty (or all whitespace) lines.
#
#   * A text block that begins with %PARAM specifies a parameter name
#     and its default value, separated by whitespace. The text in
#     the blocks that follow is the parameter description.
#
#   * The first line (text up to the first ". ") is used in Postfix
#     on-line manual pages, in the one-line configuration parameter
#     summaries.
#
#   * A text block that begins with the "<" character is treated as
#     literal HTML. For example, to specify a "dl" list element one
#     would write:
#
#         |<dt><b>name</b></dt> <dd>
#         |
#         |text that describes "name".
#         |
#         |</dd> ...
#
#     As described below, the text that describes "name" will be
#     enclosed with <p> and </p>.
#
#     An "ul" list element would be written like this:
#
#         |<li> text for this list element.
#
#   * Any text block that does not begin with < is an error.

%CLASS address-verification Address verification (Postfix 2.1 and later)

<p>
Sender/recipient address verification is implemented by sending
probe email messages that are not actually delivered. This feature
is requested via the reject_unverified_sender and
reject_unverified_recipient access restrictions.  The status of
verification probes is maintained by the address verification
service.  See the file ADDRESS_VERIFICATION_README for information
about how to configure and operate the Postfix sender/recipient
address verification service.
</p>

%CLASS smtpd-compatibility Compatibility controls

%CLASS resource-control Resource controls

%CLASS after-queue-filter After-queue content filter

<p>
As of version 1.0, Postfix can be configured to send new mail to
an external content filter AFTER the mail is queued. This content
filter is expected to inject mail back into a (Postfix or other)
MTA for further delivery.  See the FILTER_README document for
details.
</p>

%CLASS before-queue-filter Before-queue content filter

<p>
The Postfix SMTP server can be configured to send incoming mail to
a real-time SMTP-based content filter BEFORE mail is queued.  This
content filter is expected to inject mail back into Postfix.  See
the SMTPD_PROXY_README document for details on how to configure
and operate this feature.
</p>

%CLASS basic-config Basic configuration parameters

%CLASS smtpd-access-relay SMTP server access and relay control

%CLASS smtpd-sasl SMTP server SASL authentication

%CLASS unknown-recipients Rejecting mail for unknown recipients

%CLASS smtpd-reply-code SMTP server response codes

%CLASS other Other configuration parameters

%PARAM access_map_reject_code 554

<p>
The numerical Postfix SMTP server response code for
an access(5) map "reject" action.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

%PARAM access_map_defer_code 450

<p>
The numerical Postfix SMTP server response code for
an access(5) map "defer" action, including "defer_if_permit"
or "defer_if_reject". Prior to Postfix 2.6, the response
is hard-coded as "450".
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

<p>
This feature is available in Postfix 2.6 and later.
</p>

%PARAM address_verify_default_transport $default_transport

<p>
Overrides the default_transport parameter setting for address
verification probes.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_local_transport $local_transport

<p>
Overrides the local_transport parameter setting for address
verification probes.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_map see "postconf -d" output

<p>
Lookup table for persistent address verification status
storage.  The table is maintained by the verify(8) service, and
is opened before the process releases privileges.
</p>

<p>
The lookup table is persistent by default (Postfix 2.7 and later).
Specify an empty table name to keep the information in volatile
memory which is lost after "<b>postfix reload</b>" or "<b>postfix
stop</b>". This is the default with Postfix version 2.6 and earlier.
</p>

<p>
Specify a location in a file system that will not fill up. If the
database becomes corrupted, the world comes to an end. To recover
delete (NOT: truncate) the file and do "<b>postfix reload</b>".
</p>

<p> Postfix daemon processes do not use root privileges when opening
this file (Postfix 2.5 and later).  The file must therefore be
stored under a Postfix-owned directory such as the data_directory.
As a migration aid, an attempt to open the file under a non-Postfix
directory is redirected to the Postfix-owned data_directory, and a
warning is logged. </p>

<p>
Examples:
</p>

<pre>
address_verify_map = hash:/var/db/postfix/verify
address_verify_map = btree:/var/db/postfix/verify
</pre>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_negative_cache yes

<p>
Enable caching of failed address verification probe results.  When
this feature is enabled, the cache may pollute quickly with garbage.
When this feature is disabled, Postfix will generate an address
probe for every lookup.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_negative_expire_time 3d

<p>
The time after which a failed probe expires from the address
verification cache.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_negative_refresh_time 3h

<p>
The time after which a failed address verification probe needs to
be refreshed.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_cache_cleanup_interval 12h

<p> The amount of time between verify(8) address verification
database cleanup runs. This feature requires that the database
supports the "delete" and "sequence" operators.  Specify a zero
interval to disable database cleanup. </p>

<p> After each database cleanup run, the verify(8) daemon logs the
number of entries that were retained and dropped. A cleanup run is
logged as "partial" when the daemon terminates early after "<b>postfix
reload</b>", "<b>postfix stop</b>", or no requests for $max_idle
seconds. </p>

<p> Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks). </p>

<p> This feature is available in Postfix 2.7. </p>

%PARAM address_verify_poll_count ${stress?1}${stress:3}

<p>
How many times to query the verify(8) service for the completion
of an address verification request in progress.
</p>

<p> By default, the Postfix SMTP server polls the verify(8) service
up to three times under non-overload conditions, and only once when
under overload.  With Postfix version 2.6 and earlier, the SMTP
server always polls the verify(8) service up to three times by
default.  </p>

<p>
Specify 1 to implement a crude form of greylisting, that is, always
defer the first delivery request for a new address.
</p>

<p>
Examples:
</p>

<pre>
# Postfix &le; 2.6 default
address_verify_poll_count = 3
# Poor man's greylisting
address_verify_poll_count = 1
</pre>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_poll_delay 3s

<p>
The delay between queries for the completion of an address
verification request in progress.
</p>

<p>
The default polling delay is 3 seconds.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_positive_expire_time 31d

<p>
The time after which a successful probe expires from the address
verification cache.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_positive_refresh_time 7d

<p>
The time after which a successful address verification probe needs
to be refreshed.  The address verification status is not updated
when the probe fails (optimistic caching).
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_relay_transport $relay_transport

<p>
Overrides the relay_transport parameter setting for address
verification probes.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_relayhost $relayhost

<p>
Overrides the relayhost parameter setting for address verification
probes. This information can be overruled with the transport(5) table.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_sender $double_bounce_sender

<p> The sender address to use in address verification probes; prior
to Postfix 2.5 the default was "postmaster". To
avoid problems with address probes that are sent in response to
address probes, the Postfix SMTP server excludes the probe sender
address from all SMTPD access blocks. </p>

<p>
Specify an empty value (address_verify_sender =) or &lt;&gt; if you want
to use the null sender address. Beware, some sites reject mail from
&lt;&gt;, even though RFCs require that such addresses be accepted.
</p>

<p>
Examples:
</p>

<pre>
address_verify_sender = &lt;&gt;
address_verify_sender = postmaster@my.domain
</pre>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_transport_maps $transport_maps

<p>
Overrides the transport_maps parameter setting for address verification
probes.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM address_verify_virtual_transport $virtual_transport

<p>
Overrides the virtual_transport parameter setting for address
verification probes.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM alias_database see "postconf -d" output

<p>
The alias databases for local(8) delivery that are updated with
"<b>newaliases</b>" or with "<b>sendmail -bi</b>".
</p>

<p>
This is a separate configuration parameter because not all the
tables specified with $alias_maps have to be local files.
</p>

<p>
Examples:
</p>

<pre>
alias_database = hash:/etc/aliases
alias_database = hash:/etc/mail/aliases
</pre>

%PARAM alias_maps see "postconf -d" output

<p>
The alias databases that are used for local(8) delivery. See
aliases(5) for syntax details.
</p>

<p>
The default list is system dependent.  On systems with NIS, the
default is to search the local alias database, then the NIS alias
database.
</p>

<p>
If you change the alias database, run "<b>postalias /etc/aliases</b>"
(or wherever your system stores the mail alias file), or simply
run "<b>newaliases</b>" to build the necessary DBM or DB file.
</p>

<p>
The local(8) delivery agent disallows regular expression substitution
of $1 etc. in alias_maps, because that would open a security hole.
</p>

<p>
The local(8) delivery agent will silently ignore requests to use
the proxymap(8) server within alias_maps. Instead it will open the
table directly. Before Postfix version 2.2, the local(8) delivery
agent will terminate with a fatal error.
</p>

<p>
Examples:
</p>

<pre>
alias_maps = hash:/etc/aliases, nis:mail.aliases
alias_maps = hash:/etc/aliases
</pre>

%PARAM allow_mail_to_commands alias, forward

<p>
Restrict local(8) mail delivery to external commands.  The default
is to disallow delivery to "|command" in :include:  files (see
aliases(5) for the text that defines this terminology).
</p>

<p>
Specify zero or more of: <b>alias</b>, <b>forward</b> or <b>include</b>,
in order to allow commands in aliases(5), .forward files or in
:include:  files, respectively.
</p>

<p>
Example:
</p>

<pre>
allow_mail_to_commands = alias,forward,include
</pre>

%PARAM allow_mail_to_files alias, forward

<p>
Restrict local(8) mail delivery to external files. The default is
to disallow "/file/name" destinations in :include:  files (see
aliases(5) for the text that defines this terminology).
</p>

<p>
Specify zero or more of: <b>alias</b>, <b>forward</b> or <b>include</b>,
in order to allow "/file/name" destinations in aliases(5), .forward
files and in :include:  files, respectively.
</p>

<p>
Example:
</p>

<pre>
allow_mail_to_files = alias,forward,include
</pre>

%PARAM allow_min_user no

<p>
Allow a sender or recipient address to have `-' as the first
character.  By
default, this is not allowed, to avoid accidents with software that
passes email addresses via the command line. Such software
would not be able to distinguish a malicious address from a
bona fide command-line option. Although this can be prevented by
inserting a "--" option terminator into the command line, this is
difficult to enforce consistently and globally.  </p>

<p> As of Postfix version 2.5, this feature is implemented by
trivial-rewrite(8).  With earlier versions this feature was implemented
by qmgr(8) and was limited to recipient addresses only. </p>

%PARAM allow_percent_hack yes

<p>
Enable the rewriting of the form "user%domain" to "user@domain".
This is enabled by default.
</p>

<p> Note: with Postfix version 2.2, message header address rewriting
happens only when one of the following conditions is true: </p>

<ul>

<li> The message is received with the Postfix sendmail(1) command,

<li> The message is received from a network client that matches
$local_header_rewrite_clients,

<li> The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty value.

</ul>

<p> To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all". </p>

<p>
Example:
</p>

<pre>
allow_percent_hack = no
</pre>

%PARAM allow_untrusted_routing no

<p>
Forward mail with sender-specified routing (user[@%!]remote[@%!]site)
from untrusted clients to destinations matching $relay_domains.
</p>

<p>
By default, this feature is turned off.  This closes a nasty open
relay loophole where a backup MX host can be tricked into forwarding
junk mail to a primary MX host which then spams it out to the world.
</p>

<p>
This parameter also controls if non-local addresses with sender-specified
routing can match Postfix access tables. By default, such addresses
cannot match Postfix access tables, because the address is ambiguous.
</p>

%PARAM always_bcc

<p>
Optional address that receives a "blind carbon copy" of each message
that is received by the Postfix mail system.
</p>

<p>
Note: if mail to the BCC address bounces it will be returned to
the sender.
</p>

<p> Note: automatic BCC recipients are produced only for new mail.
To avoid mailer loops, automatic BCC recipients are not generated
for mail that Postfix forwards internally, nor for mail that Postfix
generates itself. </p>

%PARAM berkeley_db_create_buffer_size 16777216

<p>
The per-table I/O buffer size for programs that create Berkeley DB
hash or btree tables.  Specify a byte count.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM berkeley_db_read_buffer_size 131072

<p>
The per-table I/O buffer size for programs that read Berkeley DB
hash or btree tables.  Specify a byte count.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM best_mx_transport

<p>
Where the Postfix SMTP client should deliver mail when it detects
a "mail loops back to myself" error condition. This happens when
the local MTA is the best SMTP mail exchanger for a destination
not listed in $mydestination, $inet_interfaces, $proxy_interfaces,
$virtual_alias_domains, or $virtual_mailbox_domains.  By default,
the Postfix SMTP client returns such mail as undeliverable.
</p>

<p>
Specify, for example, "best_mx_transport = local" to pass the mail
from the Postfix SMTP client to the local(8) delivery agent. You
can specify
any message delivery "transport" or "transport:nexthop" that is
defined in the master.cf file. See the transport(5) manual page
for the syntax and meaning of "transport" or "transport:nexthop".
</p>

<p>
However, this feature is expensive because it ties up a Postfix
SMTP client process while the local(8) delivery agent is doing its
work. It is more efficient (for Postfix) to list all hosted domains
in a table or database.
</p>

%PARAM biff yes

<p>
Whether or not to use the local biff service.  This service sends
"new mail" notifications to users who have requested new mail
notification with the UNIX command "biff y".
</p>

<p>
For compatibility reasons this feature is on by default.  On systems
with lots of interactive users, the biff service can be a performance
drain.  Specify "biff = no" in main.cf to disable.
</p>

%PARAM body_checks

<p> Optional lookup tables for content inspection as specified in
the body_checks(5) manual page.  </p>

<p> Note: with Postfix versions before 2.0, these rules inspect
all content after the primary message headers. </p>

%PARAM body_checks_size_limit 51200

<p>
How much text in a message body segment (or attachment, if you
prefer to use that term) is subjected to body_checks inspection.
The amount of text is limited to avoid scanning huge attachments.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM bounce_queue_lifetime 5d

<p>
The maximal time a bounce message is queued before it is considered
undeliverable.  By default, this is the same as the queue life time
for regular mail.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).
</p>

<p>
Specify 0 when mail delivery should be tried only once.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM bounce_size_limit 50000

<p> The maximal amount of original message text that is sent in a
non-delivery notification. Specify a byte count.  A message is
returned as either message/rfc822 (the complete original) or as
text/rfc822-headers (the headers only).  With Postfix version 2.4
and earlier, a message is always returned as message/rfc822 and is
truncated when it exceeds the size limit.
</p>

<p> Notes: </p>

<ul>

<li> <p> If you increase this limit, then you should increase the
mime_nesting_limit value proportionally.  </p>

<li> <p> Be careful when making changes.  Excessively large values
will result in the loss of non-delivery notifications, when a bounce
message size exceeds a local or remote MTA's message size limit.
</p>

</ul>

%PARAM canonical_maps

<p>
Optional address mapping lookup tables for message headers and
envelopes. The mapping is applied to both sender and recipient
addresses, in both envelopes and in headers, as controlled
with the canonical_classes parameter. This is typically used
to clean up dirty addresses from legacy mail systems, or to replace
login names by Firstname.Lastname.  The table format and lookups
are documented in canonical(5). For an overview of Postfix address
manipulations see the ADDRESS_REWRITING_README document.
</p>

<p>
If you use this feature, run "<b>postmap /etc/postfix/canonical</b>" to
build the necessary DBM or DB file after every change. The changes
will become visible after a minute or so.  Use "<b>postfix reload</b>"
to eliminate the delay.
</p>

<p> Note: with Postfix version 2.2, message header address mapping
happens only when message header address rewriting is enabled: </p>

<ul>

<li> The message is received with the Postfix sendmail(1) command,

<li> The message is received from a network client that matches
$local_header_rewrite_clients,

<li> The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty value.

</ul>

<p> To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all". </p>

<p>
Examples:
</p>

<pre>
canonical_maps = dbm:/etc/postfix/canonical
canonical_maps = hash:/etc/postfix/canonical
</pre>

%PARAM canonical_classes envelope_sender, envelope_recipient, header_sender, header_recipient

<p> What addresses are subject to canonical_maps address mapping.
By default, canonical_maps address mapping is applied to envelope
sender and recipient addresses, and to header sender and header
recipient addresses.  </p>

<p> Specify one or more of: envelope_sender, envelope_recipient,
header_sender, header_recipient </p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM sender_canonical_classes envelope_sender, header_sender

<p> What addresses are subject to sender_canonical_maps address
mapping.  By default, sender_canonical_maps address mapping is
applied to envelope sender addresses, and to header sender addresses.
</p>

<p> Specify one or more of: envelope_sender, header_sender </p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM recipient_canonical_classes envelope_recipient, header_recipient

<p> What addresses are subject to recipient_canonical_maps address
mapping.  By default, recipient_canonical_maps address mapping is
applied to envelope recipient addresses, and to header recipient
addresses.  </p>

<p> Specify one or more of: envelope_recipient, header_recipient
</p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM command_directory see "postconf -d" output

<p>
The location of all postfix administrative commands.
</p>

%PARAM command_time_limit 1000s

<p>
Time limit for delivery to external commands. This limit is used
by the local(8) delivery agent, and is the default time limit for
delivery by the pipe(8) delivery agent.
</p>

<p>
Note: if you set this time limit to a large value you must update the
global ipc_timeout parameter as well.
</p>

%PARAM daemon_directory see "postconf -d" output

<p>
The directory with Postfix support programs and daemon programs.
These should not be invoked directly by humans. The directory must
be owned by root.
</p>

%PARAM daemon_timeout 18000s

<p> How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.  </p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM debug_peer_level 2

<p> The increment in verbose logging level when a remote client or
server matches a pattern in the debug_peer_list parameter.  </p>

%PARAM debug_peer_list

<p> Optional list of remote client or server hostname or network
address patterns that cause the verbose logging level to increase
by the amount specified in $debug_peer_level.  </p>

<p> Specify domain names, network/netmask patterns, "/file/name"
patterns or "type:table" lookup tables. The right-hand side result
from "type:table" lookups is ignored.  </p>

<p> Pattern matching of domain names is controlled by the
parent_domain_matches_subdomains parameter.  </p>

<p>
Examples:
</p>

<pre>
debug_peer_list = 127.0.0.1
debug_peer_list = example.com
</pre>

%PARAM default_database_type see "postconf -d" output

<p>
The default database type for use in newaliases(1), postalias(1)
and postmap(1) commands. On many UNIX systems the default type is
either <b>dbm</b> or <b>hash</b>. The default setting is frozen
when the Postfix system is built.
</p>

<p>
Examples:
</p>

<pre>
default_database_type = hash
default_database_type = dbm
</pre>

%PARAM default_delivery_slot_cost 5

<p>
How often the Postfix queue manager's scheduler is allowed to
preempt delivery of one message with another.
</p>

<p>
Each transport maintains a so-called "available delivery slot counter"
for each message. One message can be preempted by another one when
the other message can be delivered using no more delivery slots
(i.e., invocations of delivery agents) than the current message
counter has accumulated (or will eventually accumulate - see about
slot loans below). This parameter controls how often is the counter
incremented - it happens after each default_delivery_slot_cost
recipients have been delivered.
</p>

<p>
The cost of 0 is used to disable the preempting scheduling completely.
The minimum value the scheduling algorithm can use is 2 - use it
if you want to maximize the message throughput rate. Although there
is no maximum, it doesn't make much sense to use values above say
50.
</p>

<p>
The only reason why the value of 2 is not the default is the way
this parameter affects the delivery of mailing-list mail. In the
worst case, their delivery can take somewhere between (cost+1/cost)
and (cost/cost-1) times more than if the preemptive scheduler was
disabled. The default value of 5 turns out to provide reasonable
message response times while making sure the mailing-list deliveries
are not extended by more than 20-25 percent even in the worst case.
</p>

<p> Use <i>transport</i>_delivery_slot_cost to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

<p>
Examples:
</p>

<pre>
default_delivery_slot_cost = 0
default_delivery_slot_cost = 2
</pre>

%PARAM default_destination_concurrency_limit 20

<p>
The default maximal number of parallel deliveries to the same
destination.  This is the default limit for delivery via the lmtp(8),
pipe(8), smtp(8) and virtual(8) delivery agents.
With per-destination recipient limit &gt; 1, a destination is a domain,
otherwise it is a recipient.
</p>

<p> Use <i>transport</i>_destination_concurrency_limit to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

%PARAM default_destination_recipient_limit 50

<p>
The default maximal number of recipients per message delivery.
This is the default limit for delivery via the lmtp(8), pipe(8),
smtp(8) and virtual(8) delivery agents.
</p>

<p> Setting this parameter to a value of 1 changes the meaning of
the corresponding per-destination concurrency limit from concurrency
per domain into concurrency per recipient.  </p>

<p> Use <i>transport</i>_destination_recipient_limit to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

%PARAM default_extra_recipient_limit 1000

<p>
The default value for the extra per-transport limit imposed on the
number of in-memory recipients.  This extra recipient space is
reserved for the cases when the Postfix queue manager's scheduler
preempts one message with another and suddenly needs some extra
recipients slots for the chosen message in order to avoid performance
degradation.
</p>

<p> Use <i>transport</i>_extra_recipient_limit to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

%PARAM default_minimum_delivery_slots 3

<p>
How many recipients a message must have in order to invoke the
Postfix queue manager's scheduling algorithm at all.  Messages
which would never accumulate at least this many delivery slots
(subject to slot cost parameter as well) are never preempted.
</p>

<p> Use <i>transport</i>_minimum_delivery_slots to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

%PARAM default_privs nobody

<p>
The default rights used by the local(8) delivery agent for delivery
to external file or command.  These rights are used when delivery
is requested from an aliases(5) file that is owned by <b>root</b>, or
when delivery is done on behalf of <b>root</b>. <b>DO NOT SPECIFY A
PRIVILEGED USER OR THE POSTFIX OWNER</b>.
</p>

%PARAM default_process_limit 100

<p>
The default maximal number of Postfix child processes that provide
a given service. This limit can be overruled for specific services
in the master.cf file.
</p>

%PARAM default_rbl_reply see "postconf -d" output

<p>
The default SMTP server response template for a request that is
rejected by an RBL-based restriction. This template can be overruled
by specific entries in the optional rbl_reply_maps lookup table.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

<p>
The template is subject to exactly one level of $name substitution:
</p>

<dl>

<dt><b>$client</b></dt>

<dd>The client hostname and IP address, formatted as name[address]. </dd>

<dt><b>$client_address</b></dt>

<dd>The client IP address. </dd>

<dt><b>$client_name</b></dt>

<dd>The client hostname or "unknown". See reject_unknown_client_hostname
for more details. </dd>

<dt><b>$reverse_client_name</b></dt>

<dd>The client hostname from address-&gt;name lookup, or "unknown".
See reject_unknown_reverse_client_hostname for more details. </dd>

#<dt><b>$forward_client_name</b></dt>
#
#<dd>The client hostname from address-&gt;name lookup followed by
#name-&gt;address lookup, or "unknown".  See
#reject_unknown_forward_client_hostname for more details. </dd>

<dt><b>$helo_name</b></dt>

<dd>The hostname given in HELO or EHLO command or empty string. </dd>

<dt><b>$rbl_class</b></dt>

<dd>The blacklisted entity type: Client host, Helo command, Sender
address, or Recipient address. </dd>

<dt><b>$rbl_code</b></dt>

<dd>The numerical SMTP response code, as specified with the
maps_rbl_reject_code configuration parameter. Note: The numerical
SMTP response code is required, and must appear at the start of the
reply. With Postfix version 2.3 and later this information may be followed
by an RFC 3463 enhanced status code. </dd>

<dt><b>$rbl_domain</b></dt>

<dd>The RBL domain where $rbl_what is blacklisted. </dd>

<dt><b>$rbl_reason</b></dt>

<dd>The reason why $rbl_what is blacklisted, or an empty string. </dd>

<dt><b>$rbl_what</b></dt>

<dd>The entity that is blacklisted (an IP address, a hostname, a domain
name, or an email address whose domain was blacklisted). </dd>

<dt><b>$recipient</b></dt>

<dd>The recipient address or &lt;&gt; in case of the null address. </dd>

<dt><b>$recipient_domain</b></dt>

<dd>The recipient domain or empty string. </dd>

<dt><b>$recipient_name</b></dt>

<dd>The recipient address localpart or &lt;&gt; in case of null address. </dd>

<dt><b>$sender</b></dt>

<dd>The sender address or &lt;&gt; in case of the null address. </dd>

<dt><b>$sender_domain</b></dt>

<dd>The sender domain or empty string. </dd>

<dt><b>$sender_name</b></dt>

<dd>The sender address localpart or &lt;&gt; in case of the null address. </dd>

<dt><b>${name?text}</b></dt>

<dd>Expands to `text' if $name is not empty. </dd>

<dt><b>${name:text}</b></dt>

<dd>Expands to `text' if $name is empty. </dd>

</dl>

<p>
Instead of $name you can also specify ${name} or $(name).
</p>

<p> Note: when an enhanced status code is specified in an RBL reply
template, it is subject to modification.  The following transformations
are needed when the same RBL reply template is used for client,
helo, sender, or recipient access restrictions.  </p>

<ul>

<li> <p> When rejecting a sender address, the Postfix SMTP server
will transform a recipient DSN status (e.g., 4.1.1-4.1.6) into the
corresponding sender DSN status, and vice versa. </p>

<li> <p> When rejecting non-address information (such as the HELO
command argument or the client hostname/address), the Postfix SMTP
server will transform a sender or recipient DSN status into a generic
non-address DSN status (e.g., 4.0.0).  </p>

</ul>

%PARAM smtpd_expansion_filter see "postconf -d" output

<p>
The smtpd_expansion_filter configuration parameter controls what
characters may appear in $name expansions.
</p>

%PARAM default_recipient_limit 20000

<p>
The default per-transport upper limit on the number of in-memory
recipients.  These limits take priority over the global
qmgr_message_recipient_limit after the message has been assigned
to the respective transports.  See also default_extra_recipient_limit
and qmgr_message_recipient_minimum.
</p>

<p> Use <i>transport</i>_recipient_limit to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

%PARAM default_recipient_refill_limit 100

<p>
The default per-transport limit on the number of recipients refilled at
once.  When not all message recipients fit into the memory at once, keep
loading more of them in batches of at least this many at a time.  See also
$default_recipient_refill_delay, which may result in recipient batches
lower than this when this limit is too high for too slow deliveries.
</p>

<p> Use <i>transport</i>_recipient_refill_limit to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

<p> This feature is available in Postfix 2.4 and later. </p>

%PARAM default_recipient_refill_delay 5s

<p>
The default per-transport maximum delay between recipients refills.
When not all message recipients fit into the memory at once, keep loading
more of them at least once every this many seconds.  This is used to
make sure the recipients are refilled in timely manner even when
$default_recipient_refill_limit is too high for too slow deliveries.
</p>

<p> Use <i>transport</i>_recipient_refill_delay to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

<p> This feature is available in Postfix 2.4 and later. </p>

%PARAM default_transport smtp

<p>
The default mail delivery transport and next-hop destination for
destinations that do not match $mydestination, $inet_interfaces,
$proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains,
or $relay_domains.  This information can be overruled with the
sender_dependent_default_transport_maps parameter and with the
transport(5) table. </p>

<p>
In order of decreasing precedence, the nexthop destination is taken
from $sender_dependent_default_transport_maps, $default_transport,
$sender_dependent_relayhost_maps, $relayhost, or from the recipient
domain.
</p>

<p>
Specify a string of the form <i>transport:nexthop</i>, where <i>transport</i>
is the name of a mail delivery transport defined in master.cf.
The <i>:nexthop</i> destination is optional; its syntax is documented
in the manual page of the corresponding delivery agent.
</p>

<p>
Example:
</p>

<pre>
default_transport = uucp:relayhostname
</pre>

%PARAM defer_code 450

<p>
The numerical Postfix SMTP server response code when a remote SMTP
client request is rejected by the "defer" restriction.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

%PARAM defer_transports

<p>
The names of message delivery transports that should not deliver mail
unless someone issues "<b>sendmail -q</b>" or equivalent. Specify zero
or more names of mail delivery transports names that appear in the
first field of master.cf.
</p>

<p>
Example:
</p>

<pre>
defer_transports = smtp
</pre>

%PARAM deliver_lock_attempts 20

<p>
The maximal number of attempts to acquire an exclusive lock on a
mailbox file or bounce(8) logfile.
</p>

%PARAM deliver_lock_delay 1s

<p>
The time between attempts to acquire an exclusive lock on a mailbox
file or bounce(8) logfile.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM disable_vrfy_command no

<p>
Disable the SMTP VRFY command. This stops some techniques used to
harvest email addresses.
</p>

<p>
Example:
</p>

<pre>
disable_vrfy_command = no
</pre>

%PARAM double_bounce_sender double-bounce

<p> The sender address of postmaster notifications that are generated
by the mail system. All mail to this address is silently discarded,
in order to terminate mail bounce loops.  </p>

%PARAM duplicate_filter_limit 1000

<p> The maximal number of addresses remembered by the address
duplicate filter for aliases(5) or virtual(5) alias expansion, or
for showq(8) queue displays.  </p>

%PARAM enable_original_recipient yes

<p> Enable support for the X-Original-To message header. This header
is needed for multi-recipient mailboxes.  </p>

<p> When this parameter is set to yes, the cleanup(8) daemon performs
duplicate elimination on distinct pairs of (original recipient,
rewritten recipient), and generates non-empty original recipient
queue file records.  </p>

<p> When this parameter is set to no, the cleanup(8) daemon performs
duplicate elimination on the rewritten recipient address only, and
generates empty original recipient queue file records.  </p>

<p> This feature is available in Postfix 2.1 and later. With Postfix
version 2.0, support for the X-Original-To message header is always turned
on. Postfix versions before 2.0 have no support for the X-Original-To
message header.  </p>

%PARAM export_environment see "postconf -d" output

<p>
The list of environment variables that a Postfix process will export
to non-Postfix processes. The TZ variable is needed for sane
time keeping on System-V-ish systems.
</p>

<p>
Specify a list of names and/or name=value pairs, separated by
whitespace or comma. The name=value form is supported with
Postfix version 2.1 and later.
</p>

<p>
Example:
</p>

<pre>
export_environment = TZ PATH=/bin:/usr/bin
</pre>

%PARAM smtp_fallback_relay $fallback_relay

<p>
Optional list of relay hosts for SMTP destinations that can't be
found or that are unreachable. With Postfix 2.2 and earlier this
parameter is called fallback_relay.  </p>

<p>
By default, mail is returned to the sender when a destination is
not found, and delivery is deferred when a destination is unreachable.
</p>

<p> The fallback relays must be SMTP destinations. Specify a domain,
host, host:port, [host]:port, [address] or [address]:port; the form
[host] turns off MX lookups.  If you specify multiple SMTP
destinations, Postfix will try them in the specified order.  </p>

<p> To prevent mailer loops between MX hosts and fall-back hosts,
Postfix version 2.2 and later will not use the fallback relays for
destinations that it is MX host for (assuming DNS lookup is turned on).
</p>

%PARAM fallback_relay

<p>
Optional list of relay hosts for SMTP destinations that can't be
found or that are unreachable. With Postfix 2.3 this parameter
is renamed to smtp_fallback_relay. </p>

<p>
By default, mail is returned to the sender when a destination is
not found, and delivery is deferred when a destination is unreachable.
</p>

<p> The fallback relays must be SMTP destinations. Specify a domain,
host, host:port, [host]:port, [address] or [address]:port; the form
[host] turns off MX lookups.  If you specify multiple SMTP
destinations, Postfix will try them in the specified order.  </p>

<p> Note: before Postfix 2.2, do not use the fallback_relay feature
when relaying mail
for a backup or primary MX domain. Mail would loop between the
Postfix MX host and the fallback_relay host when the final destination
is unavailable. </p>

<ul>

<li> In main.cf specify "relay_transport = relay",

<li> In master.cf specify "-o fallback_relay =" (i.e., empty) at
the end of the <tt>relay</tt> entry.

<li> In transport maps, specify "relay:<i>nexthop...</i>"
as the right-hand side for backup or primary MX domain entries.

</ul>

<p> Postfix version 2.2 and later will not use the fallback_relay feature
for destinations that it is MX host for.
</p>

%PARAM fast_flush_domains $relay_domains

<p>
Optional list of destinations that are eligible for per-destination
logfiles with mail that is queued to those destinations.
</p>

<p>
By default, Postfix maintains "fast flush" logfiles only for
destinations that the Postfix SMTP server is willing to relay to
(i.e. the default is: "fast_flush_domains = $relay_domains"; see
the relay_domains parameter in the postconf(5) manual).
</p>

<p> Specify a list of hosts or domains, "/file/name" patterns or
"type:table" lookup tables, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace. A
"/file/name" pattern is replaced by its contents; a "type:table"
lookup table is matched when the domain or its parent domain appears
as lookup key.  </p>

<p>
Specify "fast_flush_domains =" (i.e., empty) to disable the feature
altogether.
</p>

%PARAM fast_flush_purge_time 7d

<p>
The time after which an empty per-destination "fast flush" logfile
is deleted.
</p>

<p>
You can specify the time as a number, or as a number followed by
a letter that indicates the time unit: s=seconds, m=minutes, h=hours,
d=days, w=weeks.  The default time unit is days.
</p>

%PARAM fast_flush_refresh_time 12h

<p>
The time after which a non-empty but unread per-destination "fast
flush" logfile needs to be refreshed.  The contents of a logfile
are refreshed by requesting delivery of all messages listed in the
logfile.
</p>

<p>
You can specify the time as a number, or as a number followed by
a letter that indicates the time unit: s=seconds, m=minutes, h=hours,
d=days, w=weeks.  The default time unit is hours.
</p>

%PARAM fork_attempts 5

<p> The maximal number of attempts to fork() a child process.  </p>

%PARAM fork_delay 1s

<p> The delay between attempts to fork() a child process.  </p>

<p> Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks).  The default time unit is s (seconds).  </p>

%PARAM execution_directory_expansion_filter see "postconf -d" output

<p> Restrict the characters that the local(8) delivery agent allows
in $name expansions of $command_execution_directory.  Characters
outside the allowed set are replaced by underscores.  </p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM command_execution_directory

<p> The local(8) delivery agent working directory for delivery to
external command.  Failure to change directory causes the delivery
to be deferred. </p>

<p> The following $name expansions are done on command_execution_directory
before the directory is changed. Expansion happens in the context
of the delivery request.  The result of $name expansion is filtered
with the character set that is specified with the
execution_directory_expansion_filter parameter.  </p>

<dl>

<dt><b>$user</b></dt>

<dd>The recipient's username. </dd>

<dt><b>$shell</b></dt>

<dd>The recipient's login shell pathname. </dd>

<dt><b>$home</b></dt>

<dd>The recipient's home directory. </dd>

<dt><b>$recipient</b></dt>

<dd>The full recipient address. </dd>

<dt><b>$extension</b></dt>

<dd>The optional recipient address extension. </dd>

<dt><b>$domain</b></dt>

<dd>The recipient domain. </dd>

<dt><b>$local</b></dt>

<dd>The entire recipient localpart. </dd>

<dt><b>$recipient_delimiter</b></dt>

<dd>The system-wide recipient address extension delimiter. </dd>

<dt><b>${name?value}</b></dt>

<dd>Expands to <i>value</i> when <i>$name</i> is non-empty. </dd>

<dt><b>${name:value}</b></dt>

<dd>Expands to <i>value</i> when <i>$name</i> is empty. </dd>

</dl>

<p>
Instead of $name you can also specify ${name} or $(name).
</p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM forward_path see "postconf -d" output

<p> The local(8) delivery agent search list for finding a .forward
file with user-specified delivery methods. The first file that is
found is used.  </p>

<p> The following $name expansions are done on forward_path before
the search actually happens. The result of $name expansion is
filtered with the character set that is specified with the
forward_expansion_filter parameter.  </p>

<dl>

<dt><b>$user</b></dt>

<dd>The recipient's username. </dd>

<dt><b>$shell</b></dt>

<dd>The recipient's login shell pathname. </dd>

<dt><b>$home</b></dt>

<dd>The recipient's home directory. </dd>

<dt><b>$recipient</b></dt>

<dd>The full recipient address. </dd>

<dt><b>$extension</b></dt>

<dd>The optional recipient address extension. </dd>

<dt><b>$domain</b></dt>

<dd>The recipient domain. </dd>

<dt><b>$local</b></dt>

<dd>The entire recipient localpart. </dd>

<dt><b>$recipient_delimiter</b></dt>

<dd>The system-wide recipient address extension delimiter. </dd>

<dt><b>${name?value}</b></dt>

<dd>Expands to <i>value</i> when <i>$name</i> is non-empty. </dd>

<dt><b>${name:value}</b></dt>

<dd>Expands to <i>value</i> when <i>$name</i> is empty. </dd>

</dl>

<p>
Instead of $name you can also specify ${name} or $(name).
</p>

<p>
Examples:
</p>

<pre>
forward_path = /var/forward/$user
forward_path =
    /var/forward/$user/.forward$recipient_delimiter$extension,
    /var/forward/$user/.forward
</pre>

%CLASS queue-hashing Queue directory hashing

<p>
Queue directory hashing is a performance feature. Splitting one
queue directory across multiple subdirectory levels can speed up
file access by reducing the number of files per directory.
</p>

<p>
Unfortunately, deeply hashing the incoming or deferred queue can
actually slow down the mail system (with a depth of 2, mailq with
an empty queue can take several seconds).
</p>

<p>
Hashing must NOT be used with a world-writable maildrop directory.
Hashing MUST be used for the defer logfile directory, to avoid poor
performance when handling lots of deferred mail.
</p>

%PARAM hash_queue_depth 1

<p>
The number of subdirectory levels for queue directories listed with
the hash_queue_names parameter.
</p>

<p>
After changing the hash_queue_names or hash_queue_depth parameter,
execute the command "<b>postfix reload</b>".
</p>

%PARAM hash_queue_names deferred, defer

<p>
The names of queue directories that are split across multiple
subdirectory levels.
</p>

<p> Before Postfix version 2.2, the default list of hashed queues
was significantly larger. Claims about improvements in file system
technology suggest that hashing of the incoming and active queues
is no longer needed. Fewer hashed directories speed up the time
needed to restart Postfix. </p>

<p>
After changing the hash_queue_names or hash_queue_depth parameter,
execute the command "<b>postfix reload</b>".
</p>

%CLASS headerbody-checks Content inspection built-in features

<p>
The Postfix cleanup(8) server has a limited ability to inspect
message headers and body content for signs of trouble. This is not
meant to be a substitute for content filters that do complex
processing such attachment decoding and unzipping.
</p>

%PARAM header_checks

<p>
Optional lookup tables for content inspection of primary non-MIME
message headers, as specified in the header_checks(5) manual page.
</p>

%PARAM header_size_limit 102400

<p>
The maximal amount of memory in bytes for storing a message header.
If a header is larger, the excess is discarded.  The limit is
enforced by the cleanup(8) server.
</p>

%PARAM home_mailbox

<p>
Optional pathname of a mailbox file relative to a local(8) user's
home directory.
</p>

<p>
Specify a pathname ending in "/" for qmail-style delivery.
</p>

<p> The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.  </p>

<p>
Examples:
</p>

<pre>
home_mailbox = Mailbox
home_mailbox = Maildir/
</pre>

%PARAM hopcount_limit 50

<p>
The maximal number of Received:  message headers that is allowed
in the primary message headers. A message that exceeds the limit
is bounced, in order to stop a mailer loop.
</p>

%PARAM ignore_mx_lookup_error no

<p> Ignore DNS MX lookups that produce no response.  By default,
the Postfix SMTP client defers delivery and tries again after some
delay.  This behavior is required by the SMTP standard.  </p>

<p>
Specify "ignore_mx_lookup_error = yes" to force a DNS A record
lookup instead. This violates the SMTP standard and can result in
mis-delivery of mail.
</p>

%PARAM import_environment see "postconf -d" output

<p>
The list of environment parameters that a Postfix process will
import from a non-Postfix parent process. Examples of relevant
parameters:
</p>

<dl>

<dt><b>TZ</b></dt>

<dd>Needed for sane time keeping on most System-V-ish systems. </dd>

<dt><b>DISPLAY</b></dt>

<dd>Needed for debugging Postfix daemons with an X-windows debugger. </dd>

<dt><b>XAUTHORITY</b></dt>

<dd>Needed for debugging Postfix daemons with an X-windows debugger. </dd>

<dt><b>MAIL_CONFIG</b></dt>

<dd>Needed to make "<b>postfix -c</b>" work. </dd>

</dl>

<p> Specify a list of names and/or name=value pairs, separated by
whitespace or comma. The name=value form is supported with
Postfix version 2.1 and later.  </p>

%PARAM in_flow_delay 1s

<p> Time to pause before accepting a new message, when the message
arrival rate exceeds the message delivery rate. This feature is
turned on by default (it's disabled on SCO UNIX due to an SCO bug).
</p>

<p>
With the default 100 SMTP server process limit, "in_flow_delay
= 1s" limits the mail inflow to 100 messages per second above the
number of messages delivered per second.
</p>

<p>
Specify 0 to disable the feature. Valid delays are 0..10.
</p>

%PARAM inet_interfaces all

<p> The network interface addresses that this mail system receives
mail on. Specify "all" to receive mail on all network
interfaces (default), and "loopback-only" to receive mail
on loopback network interfaces only (Postfix version 2.2 and later).  The
parameter also controls delivery of mail to <tt>user@[ip.address]</tt>.
</p>

<p>
Note 1: you need to stop and start Postfix when this parameter changes.
</p>

<p> Note 2: address information may be enclosed inside <tt>[]</tt>,
but this form is not required here. </p>

<p> When inet_interfaces specifies just one IPv4 and/or IPv6 address
that is not a loopback address, the Postfix SMTP client will use
this address as the IP source address for outbound mail. Support
for IPv6 is available in Postfix version 2.2 and later. </p>

<p>
On a multi-homed firewall with separate Postfix instances listening on the
"inside" and "outside" interfaces, this can prevent each instance from
being able to reach servers on the "other side" of the firewall. Setting
smtp_bind_address to 0.0.0.0 avoids the potential problem for
IPv4, and setting smtp_bind_address6 to :: solves the problem
for IPv6. </p>

<p>
A better solution for multi-homed firewalls is to leave inet_interfaces
at the default value and instead use explicit IP addresses in
the master.cf SMTP server definitions.  This preserves the Postfix
SMTP client's
loop detection, by ensuring that each side of the firewall knows that the
other IP address is still the same host. Setting $inet_interfaces to a
single IPv4 and/or IPV6 address is primarily useful with virtual
hosting of domains on
secondary IP addresses, when each IP address serves a different domain
(and has a different $myhostname setting). </p>

<p>
See also the proxy_interfaces parameter, for network addresses that
are forwarded to Postfix by way of a proxy or address translator.
</p>

<p>
Examples:
</p>

<pre>
inet_interfaces = all (DEFAULT)
inet_interfaces = loopback-only (Postfix version 2.2 and later)
inet_interfaces = 127.0.0.1
inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
inet_interfaces = 192.168.1.2, 127.0.0.1
</pre>

%PARAM inet_protocols ipv4

<p> The Internet protocols Postfix will attempt to use when making
or accepting connections. Specify one or more of "ipv4"
or "ipv6", separated by whitespace or commas. The form
"all" is equivalent to "ipv4, ipv6" or "ipv4", depending
on whether the operating system implements IPv6. </p>

<p> This feature is available in Postfix 2.2 and later. </p>

<p> Note: you MUST stop and start Postfix after changing this
parameter. </p>

<p> On systems that pre-date IPV6_V6ONLY support (RFC 3493), an
IPv6 server will also accept IPv4 connections, even when IPv4 is
turned off with the inet_protocols parameter.  On systems with
IPV6_V6ONLY support, Postfix will use separate server sockets for
IPv6 and IPv4, and each will accept only connections for the
corresponding protocol.  </p>

<p> When IPv4 support is enabled via the inet_protocols parameter,
Postfix will to DNS type A record lookups, and will convert
IPv4-in-IPv6 client IP addresses (::ffff:1.2.3.4) to their original
IPv4 form (1.2.3.4).  The latter is needed on hosts that pre-date
IPV6_V6ONLY support (RFC 3493). </p>

<p> When IPv6 support is enabled via the inet_protocols parameter,
Postfix will do DNS type AAAA record lookups. </p>

<p> When both IPv4 and IPv6 support are enabled, the Postfix SMTP
client will attempt to connect via IPv6 before attempting to use
IPv4.  </p>

<p>
Examples:
</p>

<pre>
inet_protocols = ipv4 (DEFAULT)
inet_protocols = all
inet_protocols = ipv6
inet_protocols = ipv4, ipv6
</pre>

%PARAM initial_destination_concurrency 5

<p>
The initial per-destination concurrency level for parallel delivery
to the same destination.
With per-destination recipient limit &gt; 1, a destination is a domain,
otherwise it is a recipient.
</p>

<p> Use <i>transport</i>_initial_destination_concurrency to specify
a transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport (Postfix 2.5 and later). </p>

<p>
Warning: with concurrency of 1, one bad message can be enough to
block all mail to a site.
</p>

%PARAM invalid_hostname_reject_code 501

<p>
The numerical Postfix SMTP server response code when the client
HELO or EHLO command parameter is rejected by the reject_invalid_helo_hostname
restriction.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

%PARAM ipc_idle version dependent

<p>
The time after which a client closes an idle internal communication
channel.  The purpose is to allow servers to terminate voluntarily
after they become idle. This is used, for example, by the address
resolving and rewriting clients.
</p>

<p> With Postfix 2.4 the default value was reduced from 100s to 5s. </p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM ipc_timeout 3600s

<p>
The time limit for sending or receiving information over an internal
communication channel.  The purpose is to break out of deadlock
situations. If the time limit is exceeded the software aborts with a
fatal error.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM ipc_ttl 1000s

<p>
The time after which a client closes an active internal communication
channel.  The purpose is to allow servers to terminate voluntarily
after reaching their client limit.  This is used, for example, by
the address resolving and rewriting clients.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM line_length_limit 2048

<p> Upon input, long lines are chopped up into pieces of at most
this length; upon delivery, long lines are reconstructed.  </p>

%PARAM lmtp_connect_timeout 0s

<p> The LMTP client time limit for completing a TCP connection, or
zero (use the operating system built-in time limit).  When no
connection can be made within the deadline, the LMTP client tries
the next address on the mail exchanger list.  </p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

<p>
Example:
</p>

<pre>
lmtp_connect_timeout = 30s
</pre>

%PARAM lmtp_data_done_timeout 600s

<p> The LMTP client time limit for sending the LMTP ".", and for
receiving the server response.  When no response is received within
the deadline, a warning is logged that the mail may be delivered
multiple times.  </p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM lmtp_data_init_timeout 120s

<p>
The LMTP client time limit for sending the LMTP DATA command, and
for receiving the server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM lmtp_data_xfer_timeout 180s

<p>
The LMTP client time limit for sending the LMTP message content.
When the connection stalls for more than $lmtp_data_xfer_timeout
the LMTP client terminates the transfer.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM lmtp_lhlo_timeout 300s

<p> The LMTP client time limit for receiving the LMTP greeting
banner.  When the server drops the connection without sending a
greeting banner, or when it sends no greeting banner within the
deadline, the LMTP client tries the next address on the mail
exchanger list.  </p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM lmtp_mail_timeout 300s

<p>
The LMTP client time limit for sending the MAIL FROM command, and
for receiving the server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM lmtp_quit_timeout 300s

<p>
The LMTP client time limit for sending the QUIT command, and for
receiving the server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM lmtp_rcpt_timeout 300s

<p>
The LMTP client time limit for sending the RCPT TO command, and
for receiving the server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM lmtp_rset_timeout 20s

<p> The LMTP client time limit for sending the RSET command, and
for receiving the server response. The LMTP client sends RSET in
order to finish a recipient address probe, or to verify that a
cached connection is still alive.  </p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM lmtp_send_xforward_command no

<p>
Send an XFORWARD command to the LMTP server when the LMTP LHLO
server response announces XFORWARD support.  This allows an lmtp(8)
delivery agent, used for content filter message injection, to
forward the name, address, protocol and HELO name of the original
client to the content filter and downstream queuing LMTP server.
Before you change the value to yes, it is best to make sure that
your content filter supports this command.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM lmtp_skip_quit_response no

<p>
Wait for the response to the LMTP QUIT command.
</p>

%PARAM lmtp_xforward_timeout 300s

<p>
The LMTP client time limit for sending the XFORWARD command, and
for receiving the server response.
</p>

<p>
In case of problems the client does NOT try the next address on
the mail exchanger list.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM local_command_shell

<p>
Optional shell program for local(8) delivery to non-Postfix command.
By default, non-Postfix commands are executed directly; commands
are given to given to /bin/sh only when they contain shell meta
characters or shell built-in commands.  </p>

<p> "sendmail's restricted shell" (smrsh) is what most people will
use in order to restrict what programs can be run from e.g. .forward
files (smrsh is part of the Sendmail distribution).  </p>

<p> Note: when a shell program is specified, it is invoked even
when the command contains no shell built-in commands or meta
characters.  </p>

<p>
Example:
</p>

<pre>
local_command_shell = /some/where/smrsh -c
</pre>

%PARAM local_destination_concurrency_limit 2

<p> The maximal number of parallel deliveries via the local mail
delivery transport to the same recipient (when
"local_destination_recipient_limit = 1") or the maximal number of
parallel deliveries to the same local domain (when
"local_destination_recipient_limit &gt; 1"). This limit is enforced by
the queue manager. The message delivery transport name is the first
field in the entry in the master.cf file. </p>

<p> A low limit of 2 is recommended, just in case someone has an
expensive shell command in a .forward file or in an alias (e.g.,
a mailing list manager).  You don't want to run lots of those at
the same time.  </p>

%PARAM local_destination_recipient_limit 1

<p> The maximal number of recipients per message delivery via the
local mail delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file. </p>

<p> Setting this parameter to a value &gt; 1 changes the meaning of
local_destination_concurrency_limit from concurrency per recipient
into concurrency per domain.  </p>

%PARAM local_recipient_maps proxy:unix:passwd.byname $alias_maps

<p> Lookup tables with all names or addresses of local recipients:
a recipient address is local when its domain matches $mydestination,
$inet_interfaces or $proxy_interfaces.  Specify @domain as a
wild-card for domains that do not have a valid recipient list.
Technically, tables listed with $local_recipient_maps are used as
lists: Postfix needs to know only if a lookup string is found or
not, but it does not use the result from table lookup.  </p>

<p>
If this parameter is non-empty (the default), then the Postfix SMTP
server will reject mail for unknown local users.
</p>

<p>
To turn off local recipient checking in the Postfix SMTP server,
specify "local_recipient_maps =" (i.e. empty).
</p>

<p>
The default setting assumes that you use the default Postfix local
delivery agent for local delivery. You need to update the
local_recipient_maps setting if:
</p>

<ul>

<li>You redefine the local delivery agent in master.cf.

<li>You redefine the "local_transport" setting in main.cf.

<li>You use the "luser_relay", "mailbox_transport", or "fallback_transport"
feature of the Postfix local(8) delivery agent.

</ul>

<p>
Details are described in the LOCAL_RECIPIENT_README file.
</p>

<p>
Beware: if the Postfix SMTP server runs chrooted, you need to access
the passwd file via the proxymap(8) service, in order to overcome
chroot access restrictions. The alternative, maintaining a copy of
the system password file in the chroot jail is not practical.
</p>

<p>
Examples:
</p>

<pre>
local_recipient_maps =
</pre>

%PARAM local_transport local:$myhostname

<p> The default mail delivery transport and next-hop destination
for final delivery to domains listed with mydestination, and for
[ipaddress] destinations that match $inet_interfaces or $proxy_interfaces.
This information can be overruled with the transport(5) table. </p>

<p>
By default, local mail is delivered to the transport called "local",
which is just the name of a service that is defined the master.cf file.
</p>

<p>
Specify a string of the form <i>transport:nexthop</i>, where <i>transport</i>
is the name of a mail delivery transport defined in master.cf.
The <i>:nexthop</i> destination is optional; its syntax is documented
in the manual page of the corresponding delivery agent.
</p>

<p>
Beware: if you override the default local delivery agent then you
need to review the LOCAL_RECIPIENT_README document, otherwise the
SMTP server may reject mail for local recipients.
</p>

%PARAM luser_relay

<p>
Optional catch-all destination for unknown local(8) recipients.
By default, mail for unknown recipients in domains that match
$mydestination, $inet_interfaces or $proxy_interfaces is returned
as undeliverable.
</p>

<p>
The following $name expansions are done on luser_relay:
</p>

<dl>

<dt><b>$domain</b></dt>

<dd>The recipient domain. </dd>

<dt><b>$extension</b></dt>

<dd>The recipient address extension. </dd>

<dt><b>$home</b></dt>

<dd>The recipient's home directory. </dd>

<dt><b>$local</b></dt>

<dd>The entire recipient address localpart. </dd>

<dt><b>$recipient</b></dt>

<dd>The full recipient address. </dd>

<dt><b>$recipient_delimiter</b></dt>

<dd>The system-wide recipient address extension delimiter. </dd>

<dt><b>$shell</b></dt>

<dd>The recipient's login shell. </dd>

<dt><b>$user</b></dt>

<dd>The recipient username. </dd>

<dt><b>${name?value}</b></dt>

<dd>Expands to <i>value</i> when <i>$name</i> has a non-empty value. </dd>

<dt><b>${name:value}</b></dt>

<dd>Expands to <i>value</i> when <i>$name</i> has an empty value. </dd>

</dl>

<p>
Instead of $name you can also specify ${name} or $(name).
</p>

<p>
Note: luser_relay works only for the Postfix local(8) delivery agent.
</p>

<p>
Note: if you use this feature for accounts not in the UNIX password
file, then you must specify "local_recipient_maps =" (i.e. empty)
in the main.cf file, otherwise the Postfix SMTP server will reject mail
for non-UNIX accounts with "User unknown in local recipient table".
</p>

<p>
Examples:
</p>

<pre>
luser_relay = $user@other.host
luser_relay = $local@other.host
luser_relay = admin+$local
</pre>

%PARAM mail_name Postfix

<p>
The mail system name that is displayed in Received: headers, in
the SMTP greeting banner, and in bounced mail.
</p>

%PARAM mail_owner postfix

<p>
The UNIX system account that owns the Postfix queue and most Postfix
daemon processes.  Specify the name of a user account that does
not share a group with other accounts and that owns no other files
or processes on the system.  In particular, don't specify nobody
or daemon.  PLEASE USE A DEDICATED USER ID AND GROUP ID.
</p>

<p>
When this parameter value is changed you need to re-run "<b>postfix
set-permissions</b>" (with Postfix version 2.0 and earlier:
"<b>/etc/postfix/post-install set-permissions</b>".
</p>

%PARAM mail_spool_directory see "postconf -d" output

<p>
The directory where local(8) UNIX-style mailboxes are kept. The
default setting depends on the system type. Specify a name ending
in / for maildir-style delivery.
</p>

<p>
Note: maildir delivery is done with the privileges of the recipient.
If you use the mail_spool_directory setting for maildir style
delivery, then you must create the top-level maildir directory in
advance. Postfix will not create it.
</p>

<p>
Examples:
</p>

<pre>
mail_spool_directory = /var/mail
mail_spool_directory = /var/spool/mail
</pre>

%PARAM mail_version see "postconf -d" output

<p>
The version of the mail system. Stable releases are named
<i>major</i>.<i>minor</i>.<i>patchlevel</i>. Experimental releases
also include the release date. The version string can be used in,
for example, the SMTP greeting banner.
</p>

%PARAM mailbox_command

<p>
Optional external command that the local(8) delivery agent should
use for mailbox delivery.  The command is run with the user ID and
the primary group ID privileges of the recipient.  Exception:
command delivery for root executes with $default_privs privileges.
This is not a problem, because 1) mail for root should always be
aliased to a real user and 2) don't log in as root, use "su" instead.
</p>

<p>
The following environment variables are exported to the command:
</p>

<dl>

<dt><b>CLIENT_ADDRESS</b></dt>

<dd>Remote client network address. Available in Postfix version 2.2 and
later. </dd>

<dt><b>CLIENT_HELO</b></dt>

<dd>Remote client EHLO command parameter. Available in Postfix version 2.2
and later.</dd>

<dt><b>CLIENT_HOSTNAME</b></dt>

<dd>Remote client hostname. Available in Postfix version 2.2 and later.
</dd>

<dt><b>CLIENT_PROTOCOL</b></dt>

<dd>Remote client protocol. Available in Postfix version 2.2 and later.
</dd>

<dt><b>DOMAIN</b></dt>

<dd>The domain part of the recipient address. </dd>

<dt><b>EXTENSION</b></dt>

<dd>The optional address extension. </dd>

<dt><b>HOME</b></dt>

<dd>The recipient home directory. </dd>

<dt><b>LOCAL</b></dt>

<dd>The recipient address localpart. </dd>

<dt><b>LOGNAME</b></dt>

<dd>The recipient's username. </dd>

<dt><b>ORIGINAL_RECIPIENT</b></dt>

<dd>The entire recipient address, before any address rewriting or
aliasing.  </dd>

<dt><b>RECIPIENT</b></dt>

<dd>The full recipient address. </dd>

<dt><b>SASL_METHOD</b></dt>

<dd>SASL authentication method specified in the remote client AUTH
command. Available in Postfix version 2.2 and later. </dd>

<dt><b>SASL_SENDER</b></dt>

<dd>SASL sender address specified in the remote client MAIL FROM
command. Available in Postfix version 2.2 and later. </dd>

<dt><b>SASL_USER</b></dt>

<dd>SASL username specified in the remote client AUTH command.
Available in Postfix version 2.2 and later.  </dd>

<dt><b>SENDER</b></dt>

<dd>The full sender address. </dd>

<dt><b>SHELL</b></dt>

<dd>The recipient's login shell. </dd>

<dt><b>USER</b></dt>

<dd>The recipient username. </dd>

</dl>

<p>
Unlike other Postfix configuration parameters, the mailbox_command
parameter is not subjected to $name substitutions. This is to make
it easier to specify shell syntax (see example below).
</p>

<p>
If you can, avoid shell meta characters because they will force
Postfix to run an expensive shell process. If you're delivering
via Procmail then running a shell won't make a noticeable difference
in the total cost.
</p>

<p>
Note: if you use the mailbox_command feature to deliver mail
system-wide, you must set up an alias that forwards mail for root
to a real user.
</p>

<p> The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.  </p>

<p>
Examples:
</p>

<pre>
mailbox_command = /some/where/procmail
mailbox_command = /some/where/procmail -a "$EXTENSION"
mailbox_command = /some/where/maildrop -d "$USER"
        -f "$SENDER" "$EXTENSION"
</pre>

%PARAM mailbox_size_limit 51200000

<p> The maximal size of any local(8) individual mailbox or maildir
file, or zero (no limit).  In fact, this limits the size of any
file that is written to upon local delivery, including files written
by external commands that are executed by the local(8) delivery
agent.  </p>

<p>
This limit must not be smaller than the message size limit.
</p>

%PARAM maps_rbl_reject_code 554

<p>
The numerical Postfix SMTP server response code when a remote SMTP
client request is blocked by the reject_rbl_client, reject_rhsbl_client,
reject_rhsbl_sender or reject_rhsbl_recipient restriction.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

%PARAM masquerade_classes envelope_sender, header_sender, header_recipient

<p>
What addresses are subject to address masquerading.
</p>

<p>
By default, address masquerading is limited to envelope sender
addresses, and to header sender and header recipient addresses.
This allows you to use address masquerading on a mail gateway while
still being able to forward mail to users on individual machines.
</p>

<p>
Specify zero or more of: envelope_sender, envelope_recipient,
header_sender, header_recipient
</p>

%PARAM masquerade_domains

<p>
Optional list of domains whose subdomain structure will be stripped
off in email addresses.
</p>

<p>
The list is processed left to right, and processing stops at the
first match.  Thus,
</p>

<blockquote>
<pre>
masquerade_domains = foo.example.com example.com
</pre>
</blockquote>

<p>
strips "user@any.thing.foo.example.com" to "user@foo.example.com",
but strips "user@any.thing.else.example.com" to "user@example.com".
</p>

<p>
A domain name prefixed with ! means do not masquerade this domain
or its subdomains. Thus,
</p>

<blockquote>
<pre>
masquerade_domains = !foo.example.com example.com
</pre>
</blockquote>

<p>
does not change "user@any.thing.foo.example.com" or "user@foo.example.com",
but strips "user@any.thing.else.example.com" to "user@example.com".
</p>

<p> Note: with Postfix version 2.2, message header address masquerading
happens only when message header address rewriting is enabled: </p>

<ul>

<li> The message is received with the Postfix sendmail(1) command,

<li> The message is received from a network client that matches
$local_header_rewrite_clients,

<li> The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty value.

</ul>

<p> To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all". </p>


<p>
Example:
</p>

<pre>
masquerade_domains = $mydomain
</pre>

%PARAM masquerade_exceptions

<p>
Optional list of user names that are not subjected to address
masquerading, even when their address matches $masquerade_domains.
</p>

<p>
By default, address masquerading makes no exceptions.
</p>

<p>
Specify a list of user names, "/file/name" or "type:table" patterns,
separated by commas and/or whitespace. The list is matched left to
right, and the search stops on the first match. A "/file/name"
pattern is replaced
by its contents; a "type:table" lookup table is matched when a name
matches a lookup key (the lookup result is ignored).  Continue long
lines by starting the next line with whitespace. Specify "!pattern"
to exclude a name from the list. The form "!/file/name" is supported
only in Postfix version 2.4 and later.  </p>

<p>
Examples:
</p>

<pre>
masquerade_exceptions = root, mailer-daemon
masquerade_exceptions = root
</pre>

%PARAM max_idle 100s

<p>
The maximum amount of time that an idle Postfix daemon process waits
for an incoming connection before terminating voluntarily.  This
parameter
is ignored by the Postfix queue manager and by other long-lived
Postfix daemon processes.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM max_use 100

<p>
The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.  This parameter
is ignored by the Postfix queue
manager and by other long-lived Postfix daemon processes.
</p>

%PARAM maximal_backoff_time 4000s

<p>
The maximal time between attempts to deliver a deferred message.
</p>

<p> This parameter should be set to a value greater than or equal
to $minimal_backoff_time. See also $queue_run_delay.  </p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM maximal_queue_lifetime 5d

<p>
The maximal time a message is queued before it is sent back as
undeliverable.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).
</p>

<p>
Specify 0 when mail delivery should be tried only once.
</p>

%PARAM message_size_limit 10240000

<p>
The maximal size in bytes of a message, including envelope information.
</p>

<p> Note: be careful when making changes.  Excessively small values
will result in the loss of non-delivery notifications, when a bounce
message size exceeds the local or remote MTA's message size limit.
</p>

%PARAM minimal_backoff_time 300s

<p>
The minimal time between attempts to deliver a deferred message;
prior to Postfix 2.4 the default value was 1000s.
</p>

<p>
This parameter also limits the time an unreachable destination is
kept in the short-term, in-memory, destination status cache.
</p>

<p> This parameter should be set greater than or equal to
$queue_run_delay. See also $maximal_backoff_time.  </p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM multi_recipient_bounce_reject_code 550

<p>
The numerical Postfix SMTP server response code when a remote SMTP
client request is blocked by the reject_multi_recipient_bounce
restriction.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM mydestination $myhostname, localhost.$mydomain, localhost

<p> The list of domains that are delivered via the $local_transport
mail delivery transport. By default this is the Postfix local(8)
delivery agent which looks up all recipients in /etc/passwd and
/etc/aliases. The SMTP server validates recipient addresses with
$local_recipient_maps and rejects non-existent recipients. See also
the local domain class in the ADDRESS_CLASS_README file.
</p>

<p>
The default mydestination value specifies names for the local
machine only.  On a mail domain gateway, you should also include
$mydomain.
</p>

<p>
The $local_transport delivery method is also selected for mail
addressed to user@[the.net.work.address] of the mail system (the
IP addresses specified with the inet_interfaces and proxy_interfaces
parameters).
</p>

<p>
Warnings:
</p>

<ul>

<li><p>Do not specify the names of virtual domains - those domains
are specified elsewhere. See VIRTUAL_README for more information. </p>

<li><p>Do not specify the names of domains that this machine is
backup MX host for. See STANDARD_CONFIGURATION_README for how to
set up backup MX hosts. </p>

<li><p>By default, the Postfix SMTP server rejects mail for recipients
not listed with the local_recipient_maps parameter.  See the
postconf(5) manual for a description of the local_recipient_maps
and unknown_local_recipient_reject_code parameters. </p>

</ul>

<p>
Specify a list of host or domain names, "/file/name" or "type:table"
patterns, separated by commas and/or whitespace. A "/file/name"
pattern is replaced by its contents; a "type:table" lookup table
is matched when a name matches a lookup key (the lookup result is
ignored).  Continue long lines by starting the next line with
whitespace.  </p>

<p>
Examples:
</p>

<pre>
mydestination = $myhostname, localhost.$mydomain $mydomain
mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain
</pre>

%PARAM mydomain see "postconf -d" output

<p>
The internet domain name of this mail system.  The default is to
use $myhostname minus the first component.  $mydomain is used as
a default value for many other configuration parameters.
</p>

<p>
Example:
</p>

<pre>
mydomain = domain.tld
</pre>

%PARAM myhostname see "postconf -d" output

<p>
The internet hostname of this mail system. The default is to use
the fully-qualified domain name from gethostname(). $myhostname is
used as a default value for many other configuration parameters.
</p>

<p>
Example:
</p>

<pre>
myhostname = host.example.com
</pre>

%PARAM mynetworks see "postconf -d" output

<p>
The list of "trusted" SMTP clients that have more privileges than
"strangers".
</p>

<p>
In particular, "trusted" SMTP clients are allowed to relay mail
through Postfix.  See the smtpd_recipient_restrictions parameter
description in the postconf(5) manual.
</p>

<p>
You can specify the list of "trusted" network addresses by hand
or you can let Postfix do it for you (which is the default).
See the description of the mynetworks_style parameter for more
information.
</p>

<p>
If you specify the mynetworks list by hand,
Postfix ignores the mynetworks_style setting.
</p>

<p> Specify a list of network addresses or network/netmask patterns,
separated by commas and/or whitespace. Continue long lines by
starting the next line with whitespace. </p>

<p> The netmask specifies the number of bits in the network part
of a host address.  You can also specify "/file/name" or "type:table"
patterns.  A "/file/name" pattern is replaced by its contents; a
"type:table" lookup table is matched when a table entry matches a
lookup string (the lookup result is ignored). </p>

<p> The list is matched left to right, and the search stops on the
first match.  Specify "!pattern" to exclude an address or network
block from the list. The form "!/file/name" is supported only
in Postfix version 2.4 and later. </p>

<p> Note: IP version 6 address information must be specified inside
<tt>[]</tt> in the mynetworks value, and in files specified with
"/file/name".  IP version 6 addresses contain the ":" character,
and would otherwise be confused with a "type:table" pattern.  </p>

<p> Examples:  </p>

<pre>
mynetworks = 127.0.0.0/8 168.100.189.0/28
mynetworks = !192.168.0.1, 192.168.0.0/28
mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
mynetworks = $config_directory/mynetworks
mynetworks = hash:/etc/postfix/network_table
</pre>

%PARAM myorigin $myhostname

<p>
The domain name that locally-posted mail appears to come
from, and that locally posted mail is delivered to. The default,
$myhostname, is adequate for small sites.  If you run a domain with
multiple machines, you should (1) change this to $mydomain and (2)
set up a domain-wide alias database that aliases each user to
user@that.users.mailhost.
</p>

<p>
Example:
</p>

<pre>
myorigin = $mydomain
</pre>

%PARAM notify_classes resource, software

<p>
The list of error classes that are reported to the postmaster. The
default is to report only the most serious problems. The paranoid
may wish to turn on the policy (UCE and mail relaying) and protocol
error (broken mail software) reports.
</p>

<p> NOTE: postmaster notifications may contain confidential information
such as SASL passwords or message content.  It is the system
administrator's responsibility to treat such information with care.
</p>

<p>
The error classes are:
</p>

<dl>

<dt><b>bounce</b> (also implies <b>2bounce</b>)</dt>

<dd>Send the postmaster copies of the headers of bounced mail, and
send transcripts of SMTP sessions when Postfix rejects mail. The
notification is sent to the address specified with the
bounce_notice_recipient configuration parameter (default: postmaster).
</dd>

<dt><b>2bounce</b></dt>

<dd>Send undeliverable bounced mail to the postmaster. The notification
is sent to the address specified with the 2bounce_notice_recipient
configuration parameter (default: postmaster). </dd>

<dt><b>delay</b></dt>

<dd>Send the postmaster copies of the headers of delayed mail. The
notification is sent to the address specified with the
delay_notice_recipient configuration parameter (default: postmaster).
</dd>

<dt><b>policy</b></dt>

<dd>Send the postmaster a transcript of the SMTP session when a
client request was rejected because of (UCE) policy. The notification
is sent to the address specified with the error_notice_recipient
configuration parameter (default: postmaster).  </dd>

<dt><b>protocol</b></dt>

<dd>Send the postmaster a transcript of the SMTP session in case
of client or server protocol errors. The notification is sent to
the address specified with the error_notice_recipient configuration
parameter (default: postmaster). </dd>

<dt><b>resource</b></dt>

<dd>Inform the postmaster of mail not delivered due to resource
problems.  The notification is sent to the address specified with
the error_notice_recipient configuration parameter (default:
postmaster). </dd>

<dt><b>software</b></dt>

<dd>Inform the postmaster of mail not delivered due to software
problems.  The notification is sent to the address specified with
the error_notice_recipient configuration parameter (default:
postmaster). </dd>

</dl>

<p>
Examples:
</p>

<pre>
notify_classes = bounce, delay, policy, protocol, resource, software
notify_classes = 2bounce, resource, software
</pre>

%PARAM parent_domain_matches_subdomains see "postconf -d" output

<p>
What Postfix features match subdomains of "domain.tld" automatically,
instead of requiring an explicit ".domain.tld" pattern.  This is
planned backwards compatibility:  eventually, all Postfix features
are expected to require explicit ".domain.tld" style patterns when
you really want to match subdomains.
</p>

%PARAM propagate_unmatched_extensions canonical, virtual

<p>
What address lookup tables copy an address extension from the lookup
key to the lookup result.
</p>

<p>
For example, with a virtual(5) mapping of "<i>joe@example.com =&gt;
joe.user@example.net</i>", the address "<i>joe+foo@example.com</i>"
would rewrite to "<i>joe.user+foo@example.net</i>".
</p>

<p>
Specify zero or more of <b>canonical</b>, <b>virtual</b>, <b>alias</b>,
<b>forward</b>, <b>include</b> or <b>generic</b>. These cause
address extension
propagation with canonical(5), virtual(5), and aliases(5) maps,
with local(8) .forward and :include: file lookups, and with smtp(8)
generic maps, respectively.  </p>

<p>
Note: enabling this feature for types other than <b>canonical</b>
and <b>virtual</b> is likely to cause problems when mail is forwarded
to other sites, especially with mail that is sent to a mailing list
exploder address.
</p>

<p>
Examples:
</p>

<pre>
propagate_unmatched_extensions = canonical, virtual, alias,
        forward, include
propagate_unmatched_extensions = canonical, virtual
</pre>

%PARAM proxy_interfaces

<p>
The network interface addresses that this mail system receives mail
on by way of a proxy or network address translation unit.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

<p> You must specify your "outside" proxy/NAT addresses when your
system is a backup MX host for other domains, otherwise mail delivery
loops will happen when the primary MX host is down.  </p>

<p>
Example:
</p>

<pre>
proxy_interfaces = 1.2.3.4
</pre>

%PARAM qmgr_message_active_limit 20000

<p>
The maximal number of messages in the active queue.
</p>

%PARAM qmgr_message_recipient_limit 20000

<p> The maximal number of recipients held in memory by the Postfix
queue manager, and the maximal size of the size of the short-term,
in-memory "dead" destination status cache.  </p>

%PARAM qmgr_message_recipient_minimum 10

<p>
The minimal number of in-memory recipients for any message. This
takes priority over any other in-memory recipient limits (i.e.,
the global qmgr_message_recipient_limit and the per transport
_recipient_limit) if necessary. The minimum value allowed for this
parameter is 1.
</p>

%PARAM qmqpd_authorized_clients

<p>
What clients are allowed to connect to the QMQP server port.
</p>

<p>
By default, no client is allowed to use the service. This is
because the QMQP server will relay mail to any destination.
</p>

<p>
Specify a list of client patterns. A list pattern specifies a host
name, a domain name, an internet address, or a network/mask pattern,
where the mask specifies the number of bits in the network part.
When a pattern specifies a file name, its contents are substituted
for the file name; when a pattern is a "type:table" table specification,
table lookup is used instead.  </p>

<p>
Patterns are separated by whitespace and/or commas. In order to
reverse the result, precede a pattern with an
exclamation point (!). The form "!/file/name" is supported only
in Postfix version 2.4 and later.
</p>

<p>
Example:
</p>

<pre>
qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24
</pre>

%PARAM qmqpd_error_delay 1s

<p>
How long the QMQP server will pause before sending a negative reply
to the client. The purpose is to slow down confused or malicious
clients.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM qmqpd_timeout 300s

<p>
The time limit for sending or receiving information over the network.
If a read or write operation blocks for more than $qmqpd_timeout
seconds the QMQP server gives up and disconnects.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM queue_minfree 0

<p>
The minimal amount of free space in bytes in the queue file system
that is needed to receive mail.  This is currently used by the SMTP
server to decide if it will accept any mail at all.
</p>

<p>
By default, the Postfix SMTP server rejects MAIL FROM commands when
the amount of free space is less than 1.5*$message_size_limit
(Postfix version 2.1 and later).
To specify a higher minimum free space limit, specify a queue_minfree
value that is at least 1.5*$message_size_limit.
</p>

<p>
With Postfix versions 2.0 and earlier, a queue_minfree value of
zero means there is no minimum required amount of free space.
</p>

%PARAM queue_run_delay 300s

<p>
The time between deferred queue scans by the queue manager;
prior to Postfix 2.4 the default value was 1000s.
</p>

<p> This parameter should be set less than or equal to
$minimal_backoff_time. See also $maximal_backoff_time.  </p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM rbl_reply_maps

<p>
Optional lookup tables with RBL response templates. The tables are
indexed by the RBL domain name. By default, Postfix uses the default
template as specified with the default_rbl_reply configuration
parameter. See there for a discussion of the syntax of RBL reply
templates.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM receive_override_options

<p> Enable or disable recipient validation, built-in content
filtering, or address mapping. Typically, these are specified in
master.cf as command-line arguments for the smtpd(8), qmqpd(8) or
pickup(8) daemons. </p>

<p> Specify zero or more of the following options.  The options
override main.cf settings and are either implemented by smtpd(8),
qmqpd(8), or pickup(8) themselves, or they are forwarded to the
cleanup server.  </p>

<dl>

<dt><b><a name="no_unknown_recipient_checks">no_unknown_recipient_checks</a></b></dt>

<dd>Do not try to reject unknown recipients (SMTP server only).
This is typically specified AFTER an external content filter.
</dd>

<dt><b><a name="no_address_mappings">no_address_mappings</a></b></dt>

<dd>Disable canonical address mapping, virtual alias map expansion,
address masquerading, and automatic BCC (blind carbon-copy)
recipients. This is typically specified BEFORE an external content
filter. </dd>

<dt><b><a name="no_header_body_checks">no_header_body_checks</a></b></dt>

<dd>Disable header/body_checks. This is typically specified AFTER
an external content filter. </dd>

<dt><b><a name="no_milters">no_milters</a></b></dt>

<dd>Disable Milter (mail filter) applications. This is typically
specified AFTER an external content filter. </dd>

</dl>

<p>
Note: when the "BEFORE content filter" receive_override_options
setting is specified in the main.cf file, specify the "AFTER content
filter" receive_override_options setting in master.cf (and vice
versa).
</p>

<p>
Examples:
</p>

<pre>
receive_override_options =
    no_unknown_recipient_checks, no_header_body_checks
receive_override_options = no_address_mappings
</pre>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM recipient_bcc_maps

<p>
Optional BCC (blind carbon-copy) address lookup tables, indexed by
recipient address.  The BCC address (multiple results are not
supported) is added when mail enters from outside of Postfix.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

<p>
The table search order is as follows:
</p>

<ul>

<li> Look up the "user+extension@domain.tld" address including the
optional address extension.

<li> Look up the "user@domain.tld" address without the optional
address extension.

<li> Look up the "user+extension" address local part when the
recipient domain equals $myorigin, $mydestination, $inet_interfaces
or $proxy_interfaces.

<li> Look up the "user" address local part when the recipient domain
equals $myorigin, $mydestination, $inet_interfaces or $proxy_interfaces.

<li> Look up the "@domain.tld" part.

</ul>

<p>
Specify the types and names of databases to use.  After change,
run "<b>postmap /etc/postfix/recipient_bcc</b>".
</p>

<p>
Note: if mail to the BCC address bounces it will be returned to
the sender.
</p>

<p> Note: automatic BCC recipients are produced only for new mail.
To avoid mailer loops, automatic BCC recipients are not generated
for mail that Postfix forwards internally, nor for mail that Postfix
generates itself. </p>

<p>
Example:
</p>

<pre>
recipient_bcc_maps = hash:/etc/postfix/recipient_bcc
</pre>

%PARAM recipient_canonical_maps

<p>
Optional address mapping lookup tables for envelope and header
recipient addresses.
The table format and lookups are documented in canonical(5).
</p>

<p>
Note: $recipient_canonical_maps is processed before $canonical_maps.
</p>

<p>
Example:
</p>

<pre>
recipient_canonical_maps = hash:/etc/postfix/recipient_canonical
</pre>

%PARAM recipient_delimiter

<p>
The separator between user names and address extensions (user+foo).
See canonical(5), local(8), relocated(5) and virtual(5) for the
effects this has on aliases, canonical, virtual, relocated and
on .forward file lookups.  Basically, the software tries user+foo
and .forward+foo before trying user and .forward.
</p>

<p>
Example:
</p>

<pre>
recipient_delimiter = +
</pre>

%PARAM reject_code 554

<p>
The numerical Postfix SMTP server response code when a remote SMTP
client request is rejected by the "reject" restriction.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

%PARAM relay_domains $mydestination

<p> What destination domains (and subdomains thereof) this system
will relay mail to. Subdomain matching is controlled with the
parent_domain_matches_subdomains parameter. For details about how
the relay_domains value is used, see the description of the
permit_auth_destination and reject_unauth_destination SMTP recipient
restrictions.  </p>

<p> Domains that match $relay_domains are delivered with the
$relay_transport mail delivery transport. The SMTP server validates
recipient addresses with $relay_recipient_maps and rejects non-existent
recipients. See also the relay domains address class in the
ADDRESS_CLASS_README file.  </p>

<p> Note: Postfix will not automatically forward mail for domains
that list this system as their primary or backup MX host. See the
permit_mx_backup restriction in the postconf(5) manual page.  </p>

<p> Specify a list of host or domain names, "/file/name" patterns
or "type:table" lookup tables, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace. A
"/file/name" pattern is replaced by its contents; a "type:table"
lookup table is matched when a (parent) domain appears as lookup
key. Specify "!pattern" to exclude a domain from the list. The form
"!/file/name" is supported only in Postfix version 2.4 and later.
</p>

%PARAM relay_domains_reject_code 554

<p>
The numerical Postfix SMTP server response code when a client
request is rejected by the reject_unauth_destination recipient
restriction.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

%PARAM relay_recipient_maps

<p> Optional lookup tables with all valid addresses in the domains
that match $relay_domains. Specify @domain as a wild-card for
domains that have no valid recipient list, and become a source of
backscatter mail: Postfix accepts spam for non-existent recipients
and then floods innocent people with undeliverable mail.  Technically,
tables
listed with $relay_recipient_maps are used as lists: Postfix needs
to know only if a lookup string is found or not, but it does not
use the result from table lookup.  </p>

<p>
If this parameter is non-empty, then the Postfix SMTP server will reject
mail to unknown relay users. This feature is off by default.
</p>

<p>
See also the relay domains address class in the ADDRESS_CLASS_README
file.
</p>

<p>
Example:
</p>

<pre>
relay_recipient_maps = hash:/etc/postfix/relay_recipients
</pre>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM relayhost

<p>
The next-hop destination of non-local mail; overrides non-local
domains in recipient addresses. This information is overruled with
relay_transport, sender_dependent_default_transport_maps,
default_transport, sender_dependent_relayhost_maps
and with the transport(5) table.
</p>

<p>
On an intranet, specify the organizational domain name. If your
internal DNS uses no MX records, specify the name of the intranet
gateway host instead.
</p>

<p>
In the case of SMTP, specify a domain name, hostname, hostname:port,
[hostname]:port, [hostaddress] or [hostaddress]:port. The form
[hostname] turns off MX lookups.
</p>

<p>
If you're connected via UUCP, see the UUCP_README file for useful
information.
</p>

<p>
Examples:
</p>

<pre>
relayhost = $mydomain
relayhost = [gateway.example.com]
relayhost = uucphost
relayhost = [an.ip.add.ress]
</pre>

%PARAM relocated_maps

<p>
Optional lookup tables with new contact information for users or
domains that no longer exist.  The table format and lookups are
documented in relocated(5).
</p>

<p>
If you use this feature, run "<b>postmap /etc/postfix/relocated</b>" to
build the necessary DBM or DB file after change, then "<b>postfix
reload</b>" to make the changes visible.
</p>

<p>
Examples:
</p>

<pre>
relocated_maps = dbm:/etc/postfix/relocated
relocated_maps = hash:/etc/postfix/relocated
</pre>

%PARAM require_home_directory no

<p>
Require that a local(8) recipient's home directory exists
before mail delivery is attempted. By default this test is disabled.
It can be useful for environments that import home directories to
the mail server (IMPORTING HOME DIRECTORIES IS NOT RECOMMENDED).
</p>

%PARAM resolve_dequoted_address yes

<p> Resolve a recipient address safely instead of correctly, by
looking inside quotes.  </p>

<p> By default, the Postfix address resolver does not quote the
address localpart as per RFC 822, so that additional @ or % or !
operators remain visible. This behavior is safe but it is also
technically incorrect.  </p>

<p> If you specify "resolve_dequoted_address = no", then
the Postfix
resolver will not know about additional @ etc. operators in the
address localpart. This opens opportunities for obscure mail relay
attacks with user@domain@domain addresses when Postfix provides
backup MX service for Sendmail systems.  </p>

%PARAM resolve_null_domain no

<p> Resolve an address that ends in the "@" null domain as if the
local hostname were specified, instead of rejecting the address as
invalid.  </p>

<p> This feature is available in Postfix 2.1 and later.
Earlier versions always resolve the null domain as the local
hostname.  </p>

<p> The Postfix SMTP server uses this feature to reject mail from
or to addresses that end in the "@" null domain, and from addresses
that rewrite into a form that ends in the "@" null domain.  </p>

%PARAM sender_bcc_maps

<p> Optional BCC (blind carbon-copy) address lookup tables, indexed
by sender address.  The BCC address (multiple results are not
supported) is added when mail enters from outside of Postfix.  </p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

<p>
The table search order is as follows:
</p>

<ul>

<li> Look up the "user+extension@domain.tld" address including the
optional address extension.

<li> Look up the "user@domain.tld" address without the optional
address extension.

<li> Look up the "user+extension" address local part when the
sender domain equals $myorigin, $mydestination, $inet_interfaces
or $proxy_interfaces.

<li> Look up the "user" address local part when the sender domain
equals $myorigin, $mydestination, $inet_interfaces or $proxy_interfaces.

<li> Look up the "@domain.tld" part.

</ul>

<p>
Specify the types and names of databases to use.  After change,
run "<b>postmap /etc/postfix/sender_bcc</b>".
</p>

<p>
Note: if mail to the BCC address bounces it will be returned to
the sender.
</p>

<p> Note: automatic BCC recipients are produced only for new mail.
To avoid mailer loops, automatic BCC recipients are not generated
for mail that Postfix forwards internally, nor for mail that Postfix
generates itself. </p>

<p>
Example:
</p>

<pre>
sender_bcc_maps = hash:/etc/postfix/sender_bcc
</pre>

%PARAM sender_canonical_maps

<p>
Optional address mapping lookup tables for envelope and header
sender addresses.
The table format and lookups are documented in canonical(5).
</p>

<p>
Example: you want to rewrite the SENDER address "user@ugly.domain"
to "user@pretty.domain", while still being able to send mail to
the RECIPIENT address "user@ugly.domain".
</p>

<p>
Note: $sender_canonical_maps is processed before $canonical_maps.
</p>

<p>
Example:
</p>

<pre>
sender_canonical_maps = hash:/etc/postfix/sender_canonical
</pre>

%PARAM smtp_always_send_ehlo yes

<p>
Always send EHLO at the start of an SMTP session.
</p>

<p>
With "smtp_always_send_ehlo = no", Postfix sends EHLO only when
the word "ESMTP" appears in the server greeting banner (example:
220 spike.porcupine.org ESMTP Postfix).
</p>

%PARAM smtp_bind_address

<p>
An optional numerical network address that the Postfix SMTP client
should bind to when making an IPv4 connection.
</p>

<p>
This can be specified in the main.cf file for all SMTP clients, or
it can be specified in the master.cf file for a specific client,
for example:
</p>

<blockquote>
<pre>
/etc/postfix/master.cf:
    smtp ... smtp -o smtp_bind_address=11.22.33.44
</pre>
</blockquote>

<p> Note 1: when inet_interfaces specifies no more than one IPv4
address, and that address is a non-loopback address, it is
automatically used as the smtp_bind_address.  This supports virtual
IP hosting, but can be a problem on multi-homed firewalls. See the
inet_interfaces documentation for more detail. </p>

<p> Note 2: address information may be enclosed inside <tt>[]</tt>,
but this form is not required here. </p>

%PARAM smtp_bind_address6

<p>
An optional numerical network address that the Postfix SMTP client
should bind to when making an IPv6 connection.
</p>

<p> This feature is available in Postfix 2.2 and later. </p>

<p>
This can be specified in the main.cf file for all SMTP clients, or
it can be specified in the master.cf file for a specific client,
for example:
</p>

<blockquote>
<pre>
/etc/postfix/master.cf:
    smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8
</pre>
</blockquote>

<p> Note 1: when inet_interfaces specifies no more than one IPv6
address, and that address is a non-loopback address, it is
automatically used as the smtp_bind_address6.  This supports virtual
IP hosting, but can be a problem on multi-homed firewalls. See the
inet_interfaces documentation for more detail. </p>

<p> Note 2: address information may be enclosed inside <tt>[]</tt>,
but this form is not recommended here. </p>

%PARAM smtp_connection_cache_time_limit 2s

<p> When SMTP connection caching is enabled, the amount of time that
an unused SMTP client socket is kept open before it is closed.  Do
not specify larger values without permission from the remote sites.
</p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM smtp_connection_cache_reuse_limit 10

<p> When SMTP connection caching is enabled, the number of times that
an SMTP session may be reused before it is closed.
</p>

<p> This feature is available in Postfix 2.2. In Postfix 2.3 it is
replaced by $smtp_connection_reuse_time_limit.</p>

%PARAM smtp_connection_reuse_time_limit 300s

<p> The amount of time during which Postfix will use an SMTP
connection repeatedly.  The timer starts when the connection is
initiated (i.e. it includes the connect, greeting and helo latency,
in addition to the latencies of subsequent mail delivery transactions).
</p>

<p> This feature addresses a performance stability problem with
remote SMTP servers. This problem is not specific to Postfix: it
can happen when any MTA sends large amounts of SMTP email to a site
that has multiple MX hosts. </p>

<p> The problem starts when one of a set of MX hosts becomes slower
than the rest.  Even though SMTP clients connect to fast and slow
MX hosts with equal probability, the slow MX host ends up with more
simultaneous inbound connections than the faster MX hosts, because
the slow MX host needs more time to serve each client request. </p>

<p> The slow MX host becomes a connection attractor.  If one MX
host becomes N times slower than the rest, it dominates mail delivery
latency unless there are more than N fast MX hosts to counter the
effect. And if the number of MX hosts is smaller than N, the mail
delivery latency becomes effectively that of the slowest MX host
divided by the total number of MX hosts. </p>

<p> The solution uses connection caching in a way that differs from
Postfix version 2.2.  By limiting the amount of time during which a connection
can be used repeatedly (instead of limiting the number of deliveries
over that connection), Postfix not only restores fairness in the
distribution of simultaneous connections across a set of MX hosts,
it also favors deliveries over connections that perform well, which
is exactly what we want.  </p>

<p> The default reuse time limit, 300s, is comparable to the various
smtp transaction timeouts which are fair estimates of maximum excess
latency for a slow delivery.  Note that hosts may accept thousands
of messages over a single connection within the default connection
reuse time limit. This number is much larger than the default Postfix
version 2.2 limit of 10 messages per cached connection. It may prove necessary
to lower the limit to avoid interoperability issues with MTAs that
exhibit bugs when many messages are delivered via a single connection.
A lower reuse time limit risks losing the benefit of connection
reuse when the average connection and mail delivery latency exceeds
the reuse time limit.  </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_connection_cache_destinations

<p> Permanently enable SMTP connection caching for the specified
destinations.  With SMTP connection caching, a connection is not
closed immediately after completion of a mail transaction.  Instead,
the connection is kept open for up to $smtp_connection_cache_time_limit
seconds.  This allows connections to be reused for other deliveries,
and can improve mail delivery performance. </p>

<p> Specify a comma or white space separated list of destinations
or pseudo-destinations: </p>

<ul>

<li> if mail is sent without a relay host: a domain name (the
right-hand side of an email address, without the [] around a numeric
IP address),

<li> if mail is sent via a relay host: a relay host name (without
[] or non-default TCP port), as specified in main.cf or in the
transport map,

<li> if mail is sent via a UNIX-domain socket: a pathname (without
the unix: prefix),

<li> a /file/name with domain names and/or relay host names as
defined above,

<li> a "type:table" with domain names and/or relay host names on
the left-hand side.  The right-hand side result from "type:table"
lookups is ignored.

</ul>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM smtp_connection_cache_on_demand yes

<p> Temporarily enable SMTP connection caching while a destination
has a high volume of mail in the active queue.  With SMTP connection
caching, a connection is not closed immediately after completion
of a mail transaction.  Instead, the connection is kept open for
up to $smtp_connection_cache_time_limit seconds.  This allows
connections to be reused for other deliveries, and can improve mail
delivery performance. </p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM smtp_connect_timeout 30s

<p>
The SMTP client time limit for completing a TCP connection, or
zero (use the operating system built-in time limit).
</p>

<p>
When no connection can be made within the deadline, the Postfix
SMTP client
tries the next address on the mail exchanger list. Specify 0 to
disable the time limit (i.e. use whatever timeout is implemented by
the operating system).
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM smtp_data_done_timeout 600s

<p>
The SMTP client time limit for sending the SMTP ".", and for receiving
the server response.
</p>

<p>
When no response is received within the deadline, a warning is
logged that the mail may be delivered multiple times.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM smtp_data_init_timeout 120s

<p>
The SMTP client time limit for sending the SMTP DATA command, and for
receiving the server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM smtp_data_xfer_timeout 180s

<p>
The SMTP client time limit for sending the SMTP message content.
When the connection makes no progress for more than $smtp_data_xfer_timeout
seconds the Postfix SMTP client terminates the transfer.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM smtp_defer_if_no_mx_address_found no

<p>
Defer mail delivery when no MX record resolves to an IP address.
</p>

<p>
The default (no) is to return the mail as undeliverable. With older
Postfix versions the default was to keep trying to deliver the mail
until someone fixed the MX record or until the mail was too old.
</p>

<p>
Note: Postfix always ignores MX records with equal or worse preference
than the local MTA itself.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM lmtp_destination_concurrency_limit $default_destination_concurrency_limit

<p> The maximal number of parallel deliveries to the same destination
via the lmtp message delivery transport. This limit is enforced by
the queue manager. The message delivery transport name is the first
field in the entry in the master.cf file.  </p>

%PARAM lmtp_destination_recipient_limit $default_destination_recipient_limit

<p> The maximal number of recipients per message for the lmtp
message delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file.  </p>

<p> Setting this parameter to a value of 1 changes the meaning of
lmtp_destination_concurrency_limit from concurrency per domain into
concurrency per recipient.  </p>

%PARAM relay_destination_concurrency_limit $default_destination_concurrency_limit

<p> The maximal number of parallel deliveries to the same destination
via the relay message delivery transport. This limit is enforced
by the queue manager. The message delivery transport name is the
first field in the entry in the master.cf file.  </p>

<p> This feature is available in Postfix 2.0 and later. </p>

%PARAM relay_destination_recipient_limit $default_destination_recipient_limit

<p> The maximal number of recipients per message for the relay
message delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file.  </p>

<p> Setting this parameter to a value of 1 changes the meaning of
relay_destination_concurrency_limit from concurrency per domain
into concurrency per recipient.  </p>

<p> This feature is available in Postfix 2.0 and later. </p>

%PARAM smtp_destination_concurrency_limit $default_destination_concurrency_limit

<p> The maximal number of parallel deliveries to the same destination
via the smtp message delivery transport. This limit is enforced by
the queue manager. The message delivery transport name is the first
field in the entry in the master.cf file.  </p>

%PARAM smtp_destination_recipient_limit $default_destination_recipient_limit

<p> The maximal number of recipients per message for the smtp
message delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file.  </p>

<p> Setting this parameter to a value of 1 changes the meaning of
smtp_destination_concurrency_limit from concurrency per domain
into concurrency per recipient.  </p>

%PARAM virtual_destination_concurrency_limit $default_destination_concurrency_limit

<p> The maximal number of parallel deliveries to the same destination
via the virtual message delivery transport. This limit is enforced
by the queue manager. The message delivery transport name is the
first field in the entry in the master.cf file.  </p>

%PARAM virtual_destination_recipient_limit $default_destination_recipient_limit

<p> The maximal number of recipients per message for the virtual
message delivery transport. This limit is enforced by the queue
manager. The message delivery transport name is the first field in
the entry in the master.cf file.  </p>

<p> Setting this parameter to a value of 1 changes the meaning of
virtual_destination_concurrency_limit from concurrency per domain
into concurrency per recipient.  </p>

%PARAM smtp_helo_name $myhostname

<p>
The hostname to send in the SMTP EHLO or HELO command.
</p>

<p>
The default value is the machine hostname.  Specify a hostname or
[ip.add.re.ss].
</p>

<p>
This information can be specified in the main.cf file for all SMTP
clients, or it can be specified in the master.cf file for a specific
client, for example:
</p>

<blockquote>
<pre>
/etc/postfix/master.cf:
    mysmtp ... smtp -o smtp_helo_name=foo.bar.com
</pre>
</blockquote>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM smtp_helo_timeout 300s

<p>
The SMTP client time limit for sending the HELO or EHLO command,
and for receiving the initial server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM smtp_host_lookup dns

<p>
What mechanisms the Postfix SMTP client uses to look up a host's IP
address.  This parameter is ignored when DNS lookups are disabled
(see: disable_dns_lookups).
</p>

<p>
Specify one of the following:
</p>

<dl>

<dt><b>dns</b></dt>

<dd>Hosts can be found in the DNS (preferred).  </dd>

<dt><b>native</b></dt>

<dd>Use the native naming service only (nsswitch.conf, or equivalent
mechanism).  </dd>

<dt><b>dns, native</b></dt>

<dd>Use the native service for hosts not found in the DNS.  </dd>

</dl>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtp_line_length_limit 990

<p>
The maximal length of message header and body lines that Postfix
will send via SMTP.  Longer lines are broken by inserting
"&lt;CR&gt;&lt;LF&gt;&lt;SPACE&gt;". This minimizes the damage to
MIME formatted mail.
</p>

<p>
By default, the line length is limited to 990 characters, because
some server implementations cannot receive mail with long lines.
</p>

%PARAM smtp_mail_timeout 300s

<p>
The SMTP client time limit for sending the MAIL FROM command, and
for receiving the server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM smtp_mx_address_limit 5

<p>
The maximal number of MX (mail exchanger) IP addresses that can
result from mail exchanger lookups, or zero (no limit). Prior to
Postfix version 2.3, this limit was disabled by default.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtp_mx_session_limit 2

<p> The maximal number of SMTP sessions per delivery request before
giving up or delivering to a fall-back relay host, or zero (no
limit). This restriction ignores sessions that fail to complete the
SMTP initial handshake (Postfix version 2.2 and earlier) or that fail to
complete the EHLO and TLS handshake (Postfix version 2.3 and later).  </p>

<p> This feature is available in Postfix 2.1 and later.  </p>

%PARAM smtp_never_send_ehlo no

<p> Never send EHLO at the start of an SMTP session. See also the
smtp_always_send_ehlo parameter.  </p>

%PARAM smtp_pix_workaround_threshold_time 500s

<p> How long a message must be queued before the Postfix SMTP client
turns on the PIX firewall "&lt;CR&gt;&lt;LF&gt;.&lt;CR&gt;&lt;LF&gt;"
bug workaround for delivery through firewalls with "smtp fixup"
mode turned on.  </p>

<p>
By default, the workaround is turned off for mail that is queued
for less than 500 seconds. In other words, the workaround is normally
turned off for the first delivery attempt.
</p>

<p>
Specify 0 to enable the PIX firewall
"&lt;CR&gt;&lt;LF&gt;.&lt;CR&gt;&lt;LF&gt;" bug workaround upon the
first delivery attempt.
</p>

%PARAM smtp_quit_timeout 300s

<p>
The SMTP client time limit for sending the QUIT command, and for
receiving the server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM smtp_quote_rfc821_envelope yes

<p>
Quote addresses in SMTP MAIL FROM and RCPT TO commands as required
by RFC 2821. This includes putting quotes around an address localpart
that ends in ".".
</p>

<p>
The default is to comply with RFC 2821. If you have to send mail to
a broken SMTP server, configure a special SMTP client in master.cf:
</p>

<blockquote>
<pre>
/etc/postfix/master.cf:
    broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no
</pre>
</blockquote>

<p>
and route mail for the destination in question to the "broken-smtp"
message delivery with a transport(5) table.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtp_rcpt_timeout 300s

<p>
The SMTP client time limit for sending the SMTP RCPT TO command, and
for receiving the server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM smtp_sasl_auth_enable no

<p>
Enable SASL authentication in the Postfix SMTP client.  By default,
the Postfix SMTP client uses no authentication.
</p>

<p>
Example:
</p>

<pre>
smtp_sasl_auth_enable = yes
</pre>

%PARAM smtp_sasl_password_maps

<p>
Optional SMTP client lookup tables with one username:password entry
per remote hostname or domain, or sender address when sender-dependent
authentication is enabled.  If no username:password entry is found,
then the Postfix SMTP client will not
attempt to authenticate to the remote host.
</p>

<p>
The Postfix SMTP client opens the lookup table before going to
chroot jail, so you can leave the password file in /etc/postfix.
</p>

%PARAM smtp_sasl_security_options noplaintext, noanonymous

<p> Postfix SMTP client SASL security options; as of Postfix 2.3
the list of available
features depends on the SASL client implementation that is selected
with <b>smtp_sasl_type</b>.  </p>

<p> The following security features are defined for the <b>cyrus</b>
client SASL implementation: </p>

<p>
Specify zero or more of the following:
</p>

<dl>

<dt><b>noplaintext</b></dt>

<dd>Disallow methods that use plaintext passwords. </dd>

<dt><b>noactive</b></dt>

<dd>Disallow methods subject to active (non-dictionary) attack.
</dd>

<dt><b>nodictionary</b></dt>

<dd>Disallow methods subject to passive (dictionary) attack. </dd>

<dt><b>noanonymous</b></dt>

<dd>Disallow methods that allow anonymous authentication. </dd>

<dt><b>mutual_auth</b></dt>

<dd>Only allow methods that provide mutual authentication (not
available with SASL version 1). </dd>

</dl>

<p>
Example:
</p>

<pre>
smtp_sasl_security_options = noplaintext
</pre>

%PARAM smtp_sasl_mechanism_filter

<p>
If non-empty, a Postfix SMTP client filter for the remote SMTP
server's list of offered SASL mechanisms.  Different client and
server implementations may support different mechanism lists. By
default, the Postfix SMTP client will use the intersection of the
two. smtp_sasl_mechanism_filter further restricts what server
mechanisms the client will take into consideration.  </p>

<p> Specify mechanism names, "/file/name" patterns or "type:table"
lookup tables. The right-hand side result from "type:table" lookups
is ignored. Specify "!pattern" to exclude a mechanism name from the
list. The form "!/file/name" is supported only in Postfix version
2.4 and later. </p>

<p> This feature is available in Postfix 2.2 and later. </p>

<p>
Examples:
</p>

<pre>
smtp_sasl_mechanism_filter = plain, login
smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
smtp_sasl_mechanism_filter = !gssapi, !login, static:rest
</pre>

%PARAM smtp_send_xforward_command no

<p>
Send the non-standard XFORWARD command when the Postfix SMTP server
EHLO response announces XFORWARD support.
</p>

<p>
This allows an "smtp" delivery agent, used for injecting mail into
a content filter, to forward the name, address, protocol and HELO
name of the original client to the content filter and downstream
queuing SMTP server. This can produce more useful logging than
localhost[127.0.0.1] etc.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtp_skip_4xx_greeting yes

<p>
Skip SMTP servers that greet with a 4XX status code (go away, try
again later).
</p>

<p>
By default, Postfix moves on the next mail exchanger. Specify
"smtp_skip_4xx_greeting = no" if Postfix should defer delivery
immediately.
</p>

<p> This feature is available in Postfix 2.0 and earlier.
Later Postfix versions always skip SMTP servers that greet with a
4XX status code. </p>

%PARAM smtp_skip_5xx_greeting yes

<p>
Skip SMTP servers that greet with a 5XX status code (go away, do
not try again later).
</p>

<p> By default, the Postfix SMTP client moves on the next mail
exchanger. Specify "smtp_skip_5xx_greeting = no" if Postfix should
bounce the mail immediately. The default setting is incorrect, but
it is what a lot of people expect to happen.  </p>

%PARAM smtp_skip_quit_response yes

<p>
Do not wait for the response to the SMTP QUIT command.
</p>

%PARAM smtp_xforward_timeout 300s

<p>
The SMTP client time limit for sending the XFORWARD command, and
for receiving the server response.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM authorized_verp_clients $mynetworks

<p> What SMTP clients are allowed to specify the XVERP command.
This command requests that mail be delivered one recipient at a
time with a per recipient return address.  </p>

<p> By default, only trusted clients are allowed to specify XVERP.
</p>

<p> This parameter was introduced with Postfix version 1.1.  Postfix
version 2.1 renamed this parameter to smtpd_authorized_verp_clients
and changed the default to none. </p>

<p> Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also specify hostnames or
.domain names (the initial dot causes the domain to match any name
below it),  "/file/name" or "type:table" patterns.  A "/file/name"
pattern is replaced by its contents; a "type:table" lookup table
is matched when a table entry matches a lookup string (the lookup
result is ignored).  Continue long lines by starting the next line
with whitespace. Specify "!pattern" to exclude an address or network
block from the list. The form "!/file/name" is supported only in
Postfix version 2.4 and later. </p>

<p> Note: IP version 6 address information must be specified inside
<tt>[]</tt> in the authorized_verp_clients value, and in files
specified with "/file/name".  IP version 6 addresses contain the
":" character, and would otherwise be confused with a "type:table"
pattern.  </p>

%PARAM smtpd_authorized_verp_clients $authorized_verp_clients

<p> What SMTP clients are allowed to specify the XVERP command.
This command requests that mail be delivered one recipient at a
time with a per recipient return address.  </p>

<p> By default, no clients are allowed to specify XVERP.  </p>

<p> This parameter was renamed with Postfix version 2.1. The default value
is backwards compatible with Postfix version 2.0.  </p>

<p> Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also specify hostnames or
.domain names (the initial dot causes the domain to match any name
below it),  "/file/name" or "type:table" patterns.  A "/file/name"
pattern is replaced by its contents; a "type:table" lookup table
is matched when a table entry matches a lookup string (the lookup
result is ignored).  Continue long lines by starting the next line
with whitespace. Specify "!pattern" to exclude an address or network
block from the list. The form "!/file/name" is supported only in
Postfix version 2.4 and later.  </p>

<p> Note: IP version 6 address information must be specified inside
<tt>[]</tt> in the smtpd_authorized_verp_clients value, and in
files specified with "/file/name".  IP version 6 addresses contain
the ":" character, and would otherwise be confused with a "type:table"
pattern.  </p>

%PARAM smtpd_authorized_xclient_hosts

<p>
What SMTP clients are allowed to use the XCLIENT feature.  This
command overrides SMTP client information that is used for access
control. Typical use is for SMTP-based content filters, fetchmail-like
programs, or SMTP server access rule testing. See the XCLIENT_README
document for details.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

<p>
By default, no clients are allowed to specify XCLIENT.
</p>

<p>
Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also specify hostnames or
.domain names (the initial dot causes the domain to match any name
below it),  "/file/name" or "type:table" patterns.  A "/file/name"
pattern is replaced by its contents; a "type:table" lookup table
is matched when a table entry matches a lookup string (the lookup
result is ignored).  Continue long lines by starting the next line
with whitespace. Specify "!pattern" to exclude an address or network
block from the list. The form "!/file/name" is supported only in
Postfix version 2.4 and later.  </p>

<p> Note: IP version 6 address information must be specified inside
<tt>[]</tt> in the smtpd_authorized_xclient_hosts value, and in
files specified with "/file/name".  IP version 6 addresses contain
the ":" character, and would otherwise be confused with a "type:table"
pattern.  </p>

%PARAM smtpd_authorized_xforward_hosts

<p>
What SMTP clients are allowed to use the XFORWARD feature.  This
command forwards information that is used to improve logging after
SMTP-based content filters. See the XFORWARD_README document for
details.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

<p>
By default, no clients are allowed to specify XFORWARD.
</p>

<p>
Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also specify hostnames or
.domain names (the initial dot causes the domain to match any name
below it),  "/file/name" or "type:table" patterns.  A "/file/name"
pattern is replaced by its contents; a "type:table" lookup table
is matched when a table entry matches a lookup string (the lookup
result is ignored).  Continue long lines by starting the next line
with whitespace. Specify "!pattern" to exclude an address or network
block from the list. The form "!/file/name" is supported only in
Postfix version 2.4 and later.  </p>

<p> Note: IP version 6 address information must be specified inside
<tt>[]</tt> in the smtpd_authorized_xforward_hosts value, and in
files specified with "/file/name".  IP version 6 addresses contain
the ":" character, and would otherwise be confused with a "type:table"
pattern.  </p>

%PARAM smtpd_banner $myhostname ESMTP $mail_name

<p>
The text that follows the 220 status code in the SMTP greeting
banner. Some people like to see the mail version advertised. By
default, Postfix shows no version.
</p>

<p>
You MUST specify $myhostname at the start of the text. This is
required by the SMTP protocol.
</p>

<p>
Example:
</p>

<pre>
smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)
</pre>

%PARAM smtpd_client_connection_count_limit 50

<p>
How many simultaneous connections any client is allowed to
make to this service.  By default, the limit is set to half
the default process limit value.
</p>

<p>
To disable this feature, specify a limit of 0.
</p>

<p>
WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.
</p>

<p>
This feature is available in Postfix 2.2 and later.
</p>

%PARAM smtpd_client_event_limit_exceptions $mynetworks

<p>
Clients that are excluded from connection count, connection rate,
or SMTP request rate restrictions. See the mynetworks parameter
description for the parameter value syntax.
</p>

<p>
By default, clients in trusted networks are excluded. Specify a
list of network blocks, hostnames or .domain names (the initial
dot causes the domain to match any name below it).
</p>

<p> Note: IP version 6 address information must be specified inside
<tt>[]</tt> in the smtpd_client_event_limit_exceptions value, and
in files specified with "/file/name".  IP version 6 addresses
contain the ":" character, and would otherwise be confused with a
"type:table" pattern.  </p>

<p>
This feature is available in Postfix 2.2 and later.
</p>

%PARAM smtpd_client_connection_rate_limit 0

<p>
The maximal number of connection attempts any client is allowed to
make to this service per time unit.  The time unit is specified
with the anvil_rate_time_unit configuration parameter.
</p>

<p>
By default, a client can make as many connections per time unit as
Postfix can accept.
</p>

<p>
To disable this feature, specify a limit of 0.
</p>

<p>
WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.
</p>

<p>
This feature is available in Postfix 2.2 and later.
</p>

<p>
Example:
</p>

<pre>
smtpd_client_connection_rate_limit = 1000
</pre>

%PARAM smtpd_client_message_rate_limit 0

<p>
The maximal number of message delivery requests that any client is
allowed to make to this service per time unit, regardless of whether
or not Postfix actually accepts those messages.  The time unit is
specified with the anvil_rate_time_unit configuration parameter.
</p>

<p>
By default, a client can send as many message delivery requests
per time unit as Postfix can accept.
</p>

<p>
To disable this feature, specify a limit of 0.
</p>

<p>
WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.
</p>

<p>
This feature is available in Postfix 2.2 and later.
</p>

<p>
Example:
</p>

<pre>
smtpd_client_message_rate_limit = 1000
</pre>

%PARAM smtpd_client_recipient_rate_limit 0

<p>
The maximal number of recipient addresses that any client is allowed
to send to this service per time unit, regardless of whether or not
Postfix actually accepts those recipients.  The time unit is specified
with the anvil_rate_time_unit configuration parameter.
</p>

<p>
By default, a client can send as many recipient addresses per time
unit as Postfix can accept.
</p>

<p>
To disable this feature, specify a limit of 0.
</p>

<p>
WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.
</p>

<p>
This feature is available in Postfix 2.2 and later.
</p>

<p>
Example:
</p>

<pre>
smtpd_client_recipient_rate_limit = 1000
</pre>

%PARAM smtpd_client_new_tls_session_rate_limit 0

<p>
The maximal number of new (i.e., uncached) TLS sessions that a
remote SMTP client is allowed to negotiate with this service per
time unit.  The time unit is specified with the anvil_rate_time_unit
configuration parameter.
</p>

<p>
By default, a remote SMTP client can negotiate as many new TLS
sessions per time unit as Postfix can accept.
</p>

<p>
To disable this feature, specify a limit of 0. Otherwise, specify
a limit that is at least the per-client concurrent session limit,
or else legitimate client sessions may be rejected.
</p>

<p>
WARNING: The purpose of this feature is to limit abuse. It must
not be used to regulate legitimate mail traffic.
</p>

<p>
This feature is available in Postfix 2.3 and later.
</p>

<p>
Example:
</p>

<pre>
smtpd_client_new_tls_session_rate_limit = 100
</pre>

%PARAM smtpd_client_restrictions

<p>
Optional SMTP server access restrictions in the context of a client
SMTP connection request.
See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
restriction lists" for a discussion of evaluation context and time.
</p>

<p>
The default is to allow all connection requests.
</p>

<p>
Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.
</p>

<p>
The following restrictions are specific to client hostname or
client network address information.
</p>

<dl>

<dt><b><a name="check_ccert_access">check_ccert_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd> Use the client certificate fingerprint as lookup key for the
specified access(5) database; with Postfix version 2.2, also require that
the SMTP client certificate is verified successfully.
The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to
Postfix version 2.5).  This feature is available with Postfix version
2.2 and later. </dd>

<dt><b><a name="check_client_access">check_client_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access database for the client hostname,
parent domains, client IP address, or networks obtained by stripping
least significant octets. See the access(5) manual page for details. </dd>

<dt><b><a name="check_client_mx_access">check_client_mx_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the MX hosts for the
client hostname, and execute the corresponding action.  Note: a result
of "OK" is not allowed for safety reasons. Instead, use DUNNO in order
to exclude specific hosts from blacklists.  This feature is available
in Postfix 2.7 and later.  </dd>

<dt><b><a name="check_client_ns_access">check_client_ns_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the DNS servers for
the client hostname, and execute the corresponding action.  Note: a
result of "OK" is not allowed for safety reasons. Instead, use DUNNO
in order to exclude specific hosts from blacklists.  This feature is
available in Postfix 2.7 and later.  </dd>

<dt><b><a name="check_reverse_client_hostname_access">check_reverse_client_hostname_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access database for the unverified reverse
client hostname, parent domains, client IP address, or networks
obtained by stripping least significant octets. See the access(5)
manual page for details.  Note: a result of "OK" is not allowed for
safety reasons.  Instead, use DUNNO in order to exclude specific
hosts from blacklists.  This feature is available in Postfix 2.6
and later.</dd>

<dt><b><a name="check_reverse_client_hostname_mx_access">check_reverse_client_hostname_mx_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the MX hosts for the
unverified reverse client hostname, and execute the corresponding
action.  Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from blacklists.
This feature is available in Postfix 2.7 and later.  </dd>

<dt><b><a name="check_reverse_client_hostname_ns_access">check_reverse_client_hostname_ns_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the DNS servers for
the unverified reverse client hostname, and execute the corresponding
action.  Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from blacklists.
This feature is available in Postfix 2.7 and later.  </dd>

<dt><b><a name="permit_inet_interfaces">permit_inet_interfaces</a></b></dt>

<dd>Permit the request when the client IP address matches
$inet_interfaces. </dd>

<dt><b><a name="permit_mynetworks">permit_mynetworks</a></b></dt>

<dd>Permit the request when the client IP address matches any
network or network address listed in  $mynetworks. </dd>

<dt><b><a name="permit_sasl_authenticated">permit_sasl_authenticated</a></b></dt>

<dd> Permit the request when the client is successfully
authenticated via the RFC 4954 (AUTH) protocol. </dd>


<dt><b><a name="permit_tls_all_clientcerts">permit_tls_all_clientcerts</a></b></dt>

<dd> Permit the request when the remote SMTP client certificate is
verified successfully.  This option must be used only if a special
CA issues the certificates and only this CA is listed as trusted
CA. Otherwise, clients with a third-party certificate would also
be allowed to relay.  Specify "tls_append_default_CA = no" when the
trusted CA is specified with smtpd_tls_CAfile or smtpd_tls_CApath,
to prevent Postfix from appending the system-supplied default CAs.
This feature is available with Postfix version 2.2.</dd>

<dt><b><a name="permit_tls_clientcerts">permit_tls_clientcerts</a></b></dt>

<dd>Permit the request when the remote SMTP client certificate
fingerprint is listed in $relay_clientcerts.
The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to
Postfix version 2.5).  This feature is available with Postfix version
2.2. </dd>

<dt><b><a name="reject_rbl_client">reject_rbl_client <i>rbl_domain=d.d.d.d</i></a></b></dt>

<dd>Reject the request when the reversed client network address is
listed with the A record "<i>d.d.d.d</i>" under <i>rbl_domain</i>
(Postfix version 2.1 and later only).  If no "<i>=d.d.d.d</i>" is
specified, reject the request when the reversed client network
address is listed with any A record under <i>rbl_domain</i>. <br>
The maps_rbl_reject_code parameter specifies the response code for
rejected requests (default:  554), the default_rbl_reply  parameter
specifies the default server reply, and the rbl_reply_maps  parameter
specifies tables with server replies indexed by <i>rbl_domain</i>.
This feature is available in Postfix 2.0 and later.  </dd>

<dt><b><a name="reject_rhsbl_client">reject_rhsbl_client <i>rbl_domain=d.d.d.d</i></a></b></dt>

<dd>Reject the request when the client hostname is listed with the
A record "<i>d.d.d.d</i>" under <i>rbl_domain</i> (Postfix version
2.1 and later only).  If no "<i>=d.d.d.d</i>" is specified, reject
the request when the client hostname is listed with
any A record under <i>rbl_domain</i>. See the reject_rbl_client
description above for additional RBL related configuration parameters.
This feature is available in Postfix 2.0 and later.  </dd>

<dt><b><a name="reject_unknown_client_hostname">reject_unknown_client_hostname</a></b> (with Postfix &lt; 2.3: reject_unknown_client)</dt>

<dd>Reject the request when 1) the client IP address-&gt;name mapping
fails, 2) the name-&gt;address mapping fails, or 3) the name-&gt;address
mapping does not match the client IP address.  <br> This is a
stronger restriction than the reject_unknown_reverse_client_hostname
feature, which triggers only under condition 1) above. <br> The
unknown_client_reject_code parameter specifies the response code
for rejected requests (default: 450). The reply is always 450 in
case the address-&gt;name or name-&gt;address lookup failed due to
a temporary problem. </dd>

<dt><b><a name="reject_unknown_reverse_client_hostname">reject_unknown_reverse_client_hostname</a></b></dt>

<dd>Reject the request when the client IP address has no address-&gt;name
mapping. <br> This is a weaker restriction than the
reject_unknown_client_hostname feature, which requires not only
that the address-&gt;name and name-&gt;address mappings exist, but
also that the two mappings reproduce the client IP address.  <br>
The unknown_client_reject_code parameter specifies the response
code for rejected requests (default: 450).  The reply is always 450
in case the address-&gt;name lookup failed due to a temporary
problem. <br> This feature is available in Postfix 2.3 and
later.  </dd>

#<dt><b><a name="reject_unknown_forward_client_hostname">reject_unknown_forward_client_hostname</a></b></dt>
#
#<dd>Reject the request when the client IP address has no address-&gt;name
#or name -&gt;address mapping. <br> This is a weaker restriction
#than the reject_unknown_client_hostname feature, which requires not
#only that the address-&gt;name and name-&gt;address mappings exist,
#but also that the two mappings reproduce the client IP address.
#<br> The unknown_client_reject_code parameter specifies the response
#code for rejected requests (default: 450).  The reply is always 450
#in case the address-&gt;name or name -&gt;address lookup failed due
#to a temporary problem. <br> This feature is available in Postfix
#version 2.3 and later.  </dd>

</dl>

<p>
In addition, you can use any of the following <a name="generic">
generic</a> restrictions.  These restrictions are applicable in
any SMTP command context.
</p>

<dl>

<dt><b><a name="check_policy_service">check_policy_service <i>servername</i></a></b></dt>

<dd>Query the specified policy server. See the SMTPD_POLICY_README
document for details. This feature is available in Postfix 2.1
and later. </dd>

<dt><b><a name="defer">defer</a></b></dt>

<dd>Defer the request. The client is told to try again later. This
restriction is useful at the end of a restriction list, to make
the default policy explicit. <br> The defer_code parameter specifies
the SMTP server reply code (default: 450).</dd>

<dt><b><a name="defer_if_permit">defer_if_permit</a></b></dt>

<dd>Defer the request if some later restriction would result in an
explicit or implicit PERMIT action.  This is useful when a blacklisting
feature fails due to a temporary problem.  This feature is available
in Postfix version 2.1 and later.  </dd>

<dt><b><a name="defer_if_reject">defer_if_reject</a></b></dt>

<dd>Defer the request if some later restriction would result in a
REJECT action.  This is useful when a whitelisting feature fails
due to a temporary problem.  This feature is available in Postfix
version 2.1 and later.  </dd>

<dt><b><a name="permit">permit</a></b></dt>

<dd>Permit the request. This restriction is useful at the end of
a restriction list, to make the default policy explicit.</dd>

<dt><b><a name="reject_multi_recipient_bounce">reject_multi_recipient_bounce</a></b></dt>

<dd>Reject the request when the envelope sender is the null address,
and the message has multiple envelope recipients. This usage has
rare but legitimate applications: under certain conditions,
multi-recipient mail that was posted with the DSN option NOTIFY=NEVER
may be forwarded with the null sender address.
<br> Note: this restriction can only work reliably
when used in smtpd_data_restrictions or
smtpd_end_of_data_restrictions, because the total number of
recipients is not known at an earlier stage of the SMTP conversation.
Use at the RCPT stage will only reject the second etc.  recipient.
<br>
The multi_recipient_bounce_reject_code parameter specifies the
response code for rejected requests (default:  550).  This feature
is available in Postfix 2.1 and later. </dd>

<dt><b><a name="reject_plaintext_session">reject_plaintext_session</a></b></dt>

<dd>Reject the request when the connection is not encrypted. This
restriction should not be used before the client has had a chance
to negotiate encryption with the AUTH or STARTTLS commands.
<br>
The plaintext_reject_code parameter specifies the response
code for rejected requests (default:  450).  This feature is available
in Postfix 2.3 and later. </dd>

<dt><b><a name="reject_unauth_pipelining">reject_unauth_pipelining</a></b></dt>

<dd>Reject the request when the client sends SMTP commands ahead
of time where it is not allowed, or when the client sends SMTP
commands ahead of time without knowing that Postfix actually supports
ESMTP command pipelining. This stops mail from bulk mail software
that improperly uses ESMTP command pipelining in order to speed up
deliveries.
<br> With Postfix 2.6 and later, the SMTP server sets a per-session
flag whenever it detects illegal pipelining, including pipelined
EHLO or HELO commands. The reject_unauth_pipelining feature simply
tests whether the flag was set at any point in time during the
session.
<br> With older Postfix versions, reject_unauth_pipelining checks
the current status of the input read queue, and its usage is not
recommended in contexts other than smtpd_data_restrictions.  </dd>

<dt><b><a name="reject">reject</a></b></dt>

<dd>Reject the request. This restriction is useful at the end of
a restriction list, to make the default policy explicit.  The
reject_code configuration parameter specifies the response code for
rejected requests (default: 554).</dd>

<dt><b><a name="sleep">sleep <i>seconds</i></a></b></dt>

<dd>Pause for the specified number of seconds and proceed with
the next restriction in the list, if any. This may stop zombie
mail when used as:
<pre>
/etc/postfix/main.cf:
    smtpd_client_restrictions =
        sleep 1, reject_unauth_pipelining
    smtpd_delay_reject = no
</pre>
This feature is available in Postfix 2.3. </dd>

<dt><b><a name="warn_if_reject">warn_if_reject</a></b></dt>

<dd>Change the meaning of the next restriction, so that it logs
a warning instead of rejecting a request (look for logfile records
that contain "reject_warning"). This is useful for testing new
restrictions in a "live" environment without risking unnecessary
loss of mail. </dd>

</dl>

<p>
Other restrictions that are valid in this context:
</p>

<ul>

<li> SMTP command specific restrictions that are described under
the smtpd_helo_restrictions, smtpd_sender_restrictions or
smtpd_recipient_restrictions parameters. When helo, sender or
recipient restrictions are listed under smtpd_client_restrictions,
they have effect only with "smtpd_delay_reject = yes", so that
$smtpd_client_restrictions is evaluated at the time of the RCPT TO
command.

</ul>

<p>
Example:
</p>

<pre>
smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname
</pre>

%CLASS smtpd-tarpit Tarpit features

<p>
When a remote SMTP client makes errors, the Postfix SMTP server
can insert delays before responding. This can help to slow down
run-away software.  The behavior is controlled by an error counter
that counts the number of errors within an SMTP session that a
client makes without delivering mail.
</p>

<ul>

<li><p>When the error counter is less than $smtpd_soft_error_limit the
Postfix SMTP server replies immediately (Postfix version 2.0 and earlier
delay their 4xx or 5xx error response). </p>

<li><p>When the error counter reaches $smtpd_soft_error_limit, the Postfix
SMTP server delays all its responses. </p>

<li><p>When the error counter reaches $smtpd_hard_error_limit the Postfix
SMTP server breaks the connection. </p>

</ul>

%PARAM smtpd_error_sleep_time 1s

<p>With Postfix version 2.1 and later: the SMTP server response delay after
a client has made more than $smtpd_soft_error_limit errors, and
fewer than $smtpd_hard_error_limit errors, without delivering mail.
</p>

<p>With Postfix version 2.0 and earlier: the SMTP server delay before
sending a reject (4xx or 5xx) response, when the client has made
fewer than $smtpd_soft_error_limit errors without delivering
mail. </p>

%PARAM smtpd_soft_error_limit 10

<p>
The number of errors a remote SMTP client is allowed to make without
delivering mail before the Postfix SMTP server slows down all its
responses.
</p>

<ul>

<li><p>With Postfix version 2.1 and later, the Postfix SMTP server
delays all responses by $smtpd_error_sleep_time seconds. </p>

<li><p>With Postfix versions 2.0 and earlier, the Postfix SMTP
server delays all responses by (number of errors) seconds. </p>

</ul>

%PARAM smtpd_hard_error_limit normal: 20, stress: 1

<p>
The maximal number of errors a remote SMTP client is allowed to
make without delivering mail. The Postfix SMTP server disconnects
when the limit is exceeded. Normally the default limit is 20, but
it changes under overload to just 1 with Postfix 2.6 and later.
</p>

%PARAM smtpd_junk_command_limit normal: 100, stress: 1

<p>
The number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote
SMTP client can send before the Postfix SMTP server starts to
increment the error counter with each junk command.  The junk
command count is reset after mail is delivered.  See also the
smtpd_error_sleep_time and smtpd_soft_error_limit configuration
parameters.  Normally the default limit is 100, but it changes under
overload to just 1 with Postfix 2.6 and later.
</p>

%PARAM smtpd_recipient_overshoot_limit 1000

<p> The number of recipients that a remote SMTP client can send in
excess of the limit specified with $smtpd_recipient_limit, before
the Postfix SMTP server increments the per-session error count
for each excess recipient.  </p>

%PARAM smtpd_etrn_restrictions

<p>
Optional SMTP server access restrictions in the context of a client
ETRN request.
See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
restriction lists" for a discussion of evaluation context and time.
</p>

<p>
The Postfix ETRN implementation accepts only destinations that are
eligible for the Postfix "fast flush" service. See the ETRN_README
file for details.
</p>

<p>
Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.
</p>

<p>
The following restrictions are specific to the domain name information
received with the ETRN command.
</p>

<dl>

<dt><b><a name="check_etrn_access">check_etrn_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access database for the ETRN domain name
or its parent domains. See the access(5) manual page for details.
</dd>

</dl>

<p>
Other restrictions that are valid in this context:
</p>

<ul>

<li><a href="#generic">Generic</a> restrictions that can be used
in any SMTP command context, described under smtpd_client_restrictions.

<li>SMTP command specific restrictions described under
smtpd_client_restrictions and smtpd_helo_restrictions.

</ul>

<p>
Example:
</p>

<pre>
smtpd_etrn_restrictions = permit_mynetworks, reject
</pre>

%PARAM smtpd_expansion_filter see "postconf -d" output

<p>
What characters are allowed in $name expansions of RBL reply
templates. Characters not in the allowed set are replaced by "_".
Use C like escapes to specify special characters such as whitespace.
</p>

<p>
This parameter is not subjected to $parameter expansion.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM smtpd_forbidden_commands CONNECT, GET, POST

<p>
List of commands that causes the Postfix SMTP server to immediately
terminate the session with a 221 code. This can be used to disconnect
clients that obviously attempt to abuse the system. In addition to the
commands listed in this parameter, commands that follow the "Label:"
format of message headers will also cause a disconnect.
</p>

<p>
This feature is available in Postfix 2.2 and later.
</p>

%PARAM smtpd_helo_required no

<p>
Require that a remote SMTP client introduces itself with the HELO
or EHLO command before sending the MAIL command or other commands
that require EHLO negotiation.
</p>

<p>
Example:
</p>

<pre>
smtpd_helo_required = yes
</pre>

%PARAM smtpd_helo_restrictions

<p>
Optional restrictions that the Postfix SMTP server applies in the
context of the SMTP HELO command.
See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
restriction lists" for a discussion of evaluation context and time.
</p>

<p>
The default is to permit everything.
</p>

<p>
Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.
</p>

<p>
The following restrictions are specific to the hostname information
received with the HELO or EHLO command.
</p>

<dl>

<dt><b><a name="check_helo_access">check_helo_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the HELO or EHLO
hostname or parent domains, and execute the corresponding action.
</dd>

<dt><b><a name="check_helo_mx_access">check_helo_mx_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the MX hosts for
the HELO or EHLO hostname, and execute the corresponding action.
Note: a result of "OK" is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from blacklists.  This
feature is available in Postfix 2.1 and later.  </dd>

<dt><b><a name="check_helo_ns_access">check_helo_ns_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the DNS servers
for the HELO or EHLO hostname, and execute the corresponding action.
Note: a result of "OK" is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from blacklists.  This
feature is available in Postfix 2.1 and later.  </dd>

<dt><b><a name="reject_invalid_helo_hostname">reject_invalid_helo_hostname</a></b> (with Postfix &lt; 2.3: reject_invalid_hostname)</dt>

<dd>Reject the request when the HELO or EHLO hostname syntax is
invalid. <br> The invalid_hostname_reject_code specifies the response
code for rejected requests (default: 501).</dd>

<dt><b><a name="reject_non_fqdn_helo_hostname">reject_non_fqdn_helo_hostname</a></b> (with Postfix &lt; 2.3: reject_non_fqdn_hostname)</dt>

<dd>Reject the request when the HELO or EHLO hostname is not in
fully-qualified domain form, as required by the RFC. <br> The
non_fqdn_reject_code parameter specifies the response code for
rejected requests (default: 504).</dd>

<dt><b><a name="reject_rhsbl_helo">reject_rhsbl_helo <i>rbl_domain=d.d.d.d</i></a></b></dt>

<dd>Reject the request when the HELO or EHLO hostname hostname is
listed with the A record "<i>d.d.d.d</i>" under <i>rbl_domain</i>
(Postfix version 2.1 and later only).  If no "<i>=d.d.d.d</i>" is
specified, reject the request when the HELO or EHLO hostname is
listed with any A record under <i>rbl_domain</i>. See the
reject_rbl_client description for additional RBL related configuration
parameters.  This feature is available in Postfix 2.0 and later.
</dd>

<dt><b><a name="reject_unknown_helo_hostname">reject_unknown_helo_hostname</a></b> (with Postfix &lt; 2.3: reject_unknown_hostname)</dt>

<dd>Reject the request when the HELO or EHLO hostname has no DNS A
or MX record. <br> The unknown_hostname_reject_code parameter
specifies the numerical response code for rejected requests (default:
450). <br> The unknown_helo_hostname_tempfail_action parameter
specifies the action after a temporary DNS error (default:
defer_if_permit). </dd>

</dl>

<p>
Other restrictions that are valid in this context:
</p>

<ul>

<li> <a href="#generic">Generic</a> restrictions that can be used
in any SMTP command context, described under smtpd_client_restrictions.

<li> Client hostname or network address specific restrictions
described under smtpd_client_restrictions.

<li> SMTP command specific restrictions described under
smtpd_sender_restrictions or smtpd_recipient_restrictions.  When
sender or recipient restrictions are listed under smtpd_helo_restrictions,
they have effect only with "smtpd_delay_reject = yes", so that
$smtpd_helo_restrictions is evaluated at the time of the RCPT TO
command.

</ul>

<p>
Examples:
</p>

<pre>
smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname
</pre>

%PARAM smtpd_history_flush_threshold 100

<p>
The maximal number of lines in the Postfix SMTP server command history
before it is flushed upon receipt of EHLO, RSET, or end of DATA.
</p>

%PARAM smtpd_noop_commands

<p>
List of commands that the Postfix SMTP server replies to with "250
Ok", without doing any syntax checks and without changing state.
This list overrides any commands built into the Postfix SMTP server.
</p>

%PARAM smtpd_proxy_ehlo $myhostname

<p>
How the Postfix SMTP server announces itself to the proxy filter.
By default, the Postfix hostname is used.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtpd_proxy_options

<p>
List of options that control how the Postfix SMTP server
communicates with a before-queue content filter. Specify zero or
more of the following, separated by comma or whitespace.  </p>

<dl>

<dt><b>speed_adjust</b></dt>

<dd> <p> Do not connect to a before-queue content filter until an entire
message has been received. This reduces the number of simultaneous
before-queue content filter processes. </p>

<p> NOTE 1: A filter must not <i>selectively</i> reject recipients
of a multi-recipient message.  Rejecting all recipients is OK, as
is accepting all recipients. </p>

<p> NOTE 2: This feature increases the minimum amount of free queue
space by $message_size_limit. The extra space is needed to save the
message to a temporary file. </p> </dd>

</dl>

<p>
This feature is available in Postfix 2.7 and later.
</p>

%CLASS smtpd-proxy SMTP Proxy filter

<p>
As of Postfix version 2.1, the SMTP server can forward all incoming
mail to a content filtering proxy server that inspects all mail
BEFORE it is stored in the Postfix mail queue.
</p>

<p>
WARNING: the proxy filter must reply within a fixed deadline or
else the remote SMTP client times out and mail duplication happens.
This becomes a problem as mail load increases so that fewer and
fewer CPU cycles remain available to mead the fixed deadline.
</p>

%PARAM smtpd_proxy_filter

<p> The hostname and TCP port of the mail filtering proxy server.
The proxy receives all mail from the Postfix SMTP server, and is
supposed to give the result to another Postfix SMTP server process.
</p>

<p> Specify "host:port" or "inet:host:port" for a TCP endpoint, or
"unix:pathname" for a UNIX-domain endpoint. The host can be specified
as an IP address or as a symbolic name; no MX lookups are done.
When no "host" or "host:"  are specified, the local machine is
assumed.  Pathname interpretation is relative to the Postfix queue
directory.  </p>

<p> This feature is available in Postfix 2.1 and later.  </p>

<p> The "inet:" and "unix:" prefixes are available in Postfix 2.3
and later.  </p>

%PARAM smtpd_proxy_timeout 100s

<p>
The time limit for connecting to a proxy filter and for sending or
receiving information.  When a connection fails the client gets a
generic error message while more detailed information is logged to
the maillog file.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtpd_recipient_limit 1000

<p>
The maximal number of recipients that the Postfix SMTP server
accepts per message delivery request.
</p>

%PARAM smtpd_recipient_restrictions permit_mynetworks, reject_unauth_destination

<p>
The access restrictions that the Postfix SMTP server applies in
the context of the RCPT TO command.
See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
restriction lists" for a discussion of evaluation context and time.
</p>

<p>
By default, the Postfix SMTP server accepts:
</p>

<ul>

<li> Mail from clients whose IP address matches $mynetworks, or:

<li> Mail to remote destinations that match $relay_domains, except
for addresses that contain sender-specified routing
(user@elsewhere@domain), or:

<li> Mail to local destinations that match $inet_interfaces
or $proxy_interfaces, $mydestination, $virtual_alias_domains, or
$virtual_mailbox_domains.

</ul>

<p>
IMPORTANT: If you change this parameter setting, you must specify
at least one of the following restrictions. Otherwise Postfix will
refuse to receive mail:
</p>

<blockquote>
<pre>
reject, defer, defer_if_permit, reject_unauth_destination
</pre>
</blockquote>

<p>
Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.
</p>

<p>
The following restrictions are specific to the recipient address
that is received with the RCPT TO command.
</p>

<dl>

<dt><b><a name="check_recipient_access">check_recipient_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the resolved RCPT
TO address, domain, parent domains, or localpart@, and execute the
corresponding action.  </dd>

<dt><b><a name="check_recipient_mx_access">check_recipient_mx_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the MX hosts for
the RCPT TO domain, and execute the corresponding action.  Note:
a result of "OK" is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from blacklists.  This
feature is available in Postfix 2.1 and later. </dd>

<dt><b><a name="check_recipient_ns_access">check_recipient_ns_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the DNS servers
for the RCPT TO domain, and execute the corresponding action.
Note: a result of "OK" is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from blacklists.  This
feature is available in Postfix 2.1 and later.  </dd>

<dt><b><a name="permit_auth_destination">permit_auth_destination</a></b></dt>

<dd>Permit the request when one of the following is true:

<ul>

<li> Postfix is mail forwarder: the resolved RCPT TO domain matches
$relay_domains or a subdomain thereof, and the address contains no
sender-specified routing (user@elsewhere@domain),

<li> Postfix is the final destination: the resolved RCPT TO domain
matches $mydestination, $inet_interfaces, $proxy_interfaces,
$virtual_alias_domains, or $virtual_mailbox_domains, and the address
contains no sender-specified routing (user@elsewhere@domain).

</ul></dd>

<dt><b><a name="permit_mx_backup">permit_mx_backup</a></b></dt>

<dd>Permit the request when the local mail system is backup MX for
the RCPT TO domain, or when the domain is an authorized destination
(see permit_auth_destination for definition).

<ul>

<li> Safety: permit_mx_backup does not accept addresses that have
sender-specified routing information (example: user@elsewhere@domain).

<li> Safety: permit_mx_backup can be vulnerable to mis-use when
access is not restricted with permit_mx_backup_networks.

<li> Safety: as of Postfix version 2.3, permit_mx_backup no longer
accepts the address when the local mail system is primary MX for
the recipient domain.  Exception: permit_mx_backup accepts the address
when it specifies an authorized destination (see permit_auth_destination
for definition).

<li> Limitation: mail may be rejected in case of a temporary DNS
lookup problem with Postfix prior to version 2.0.

</ul></dd>

<dt><b><a name="reject_non_fqdn_recipient">reject_non_fqdn_recipient</a></b></dt>

<dd>Reject the request when the RCPT TO address is not in
fully-qualified domain form, as required by the RFC. <br> The
non_fqdn_reject_code parameter specifies the response code for
rejected requests (default: 504). </dd>

<dt><b><a name="reject_rhsbl_recipient">reject_rhsbl_recipient <i>rbl_domain=d.d.d.d</i></a></b></dt>

<dd>Reject the request when the RCPT TO domain is listed with the
A record "<i>d.d.d.d</i>" under <i>rbl_domain</i> (Postfix version
2.1 and later only).  If no "<i>=d.d.d.d</i>" is specified, reject
the request when the RCPT TO domain is listed with
any A record under <i>rbl_domain</i>. <br> The maps_rbl_reject_code
parameter specifies the response code for rejected requests (default:
554); the default_rbl_reply parameter specifies the default server
reply; and the rbl_reply_maps parameter specifies tables with server
replies indexed by <i>rbl_domain</i>.  This feature is available
in Postfix version 2.0 and later.</dd>

<dt><b><a name="reject_unauth_destination">reject_unauth_destination</a></b></dt>

<dd>Reject the request unless one of the following is true:

<ul>

<li> Postfix is mail forwarder: the resolved RCPT TO domain matches
$relay_domains or a subdomain thereof, and contains no sender-specified
routing (user@elsewhere@domain),

<li> Postfix is the final destination: the resolved RCPT TO domain
matches $mydestination, $inet_interfaces, $proxy_interfaces,
$virtual_alias_domains, or $virtual_mailbox_domains, and contains
no sender-specified routing (user@elsewhere@domain).

</ul> The relay_domains_reject_code parameter specifies the response
code for rejected requests (default: 554). </dd>

<dt><b><a name="reject_unknown_recipient_domain">reject_unknown_recipient_domain</a></b></dt>

<dd>Reject the request when Postfix is not final destination for
the recipient domain, and the RCPT TO domain has no DNS A or MX
record, or when it has a malformed MX record such as a record with
a zero-length MX hostname (Postfix version 2.3 and later). <br> The
unknown_address_reject_code parameter specifies the numerical
response code for rejected requests (default: 450).  The response
is always 450 in case of a temporary DNS error. <br> The
unknown_address_tempfail_action parameter specifies the action
after a temporary DNS error (default: defer_if_permit).  </dd>

<dt><b><a name="reject_unlisted_recipient">reject_unlisted_recipient</a></b> (with Postfix version 2.0: check_recipient_maps)</dt>

<dd> Reject the request when the RCPT TO address is not listed in
the list of valid recipients for its domain class. See the
smtpd_reject_unlisted_recipient parameter description for details.
This feature is available in Postfix 2.1 and later.</dd>

<dt><b><a name="reject_unverified_recipient">reject_unverified_recipient</a></b></dt>

<dd>Reject the request when mail to the RCPT TO address is known
to bounce, or when the recipient address destination is not reachable.
Address verification information is managed by the verify(8) server;
see the ADDRESS_VERIFICATION_README file for details.  <br> The
unverified_recipient_reject_code parameter specifies the numerical
response code when an address is known to bounce (default: 450,
change into 550 when you are confident that it is safe to do so).
<br>The unverified_recipient_defer_code parameter specifies the
numerical response code when an address probe failed due to a
temporary problem (default: 450). <br> The
unverified_recipient_tempfail_action parameter specifies the action
after addres probe failure due to a temporary problem (default:
defer_if_permit).  <br>  This feature is available in Postfix 2.1
and later.  </dd>

</dl>

<p>
Other restrictions that are valid in this context:
</p>

<ul>

<li><a href="#generic">Generic</a> restrictions that can be used
in any SMTP command context, described under smtpd_client_restrictions.

<li>SMTP command specific restrictions described under
smtpd_client_restrictions, smtpd_helo_restrictions and
smtpd_sender_restrictions.

</ul>

<p>
Example:
</p>

<pre>
smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination
</pre>

%CLASS sasl-auth SASL Authentication

<p>
Postfix SASL support (RFC 4954) can be used to authenticate remote
SMTP clients to the Postfix SMTP server, and to authenticate the
Postfix SMTP client to a remote SMTP server.
See the SASL_README document for details.
</p>

%PARAM smtpd_sasl_auth_enable no

<p>
Enable SASL authentication in the Postfix SMTP server. By default,
the Postfix SMTP server does not use authentication.
</p>

<p>
If a remote SMTP client is authenticated, the permit_sasl_authenticated
access restriction can be used to permit relay access, like this:
</p>

<blockquote>
<pre>
smtpd_recipient_restrictions =
    permit_mynetworks, permit_sasl_authenticated, ...
</pre>
</blockquote>

<p> To reject all SMTP connections from unauthenticated clients,
specify "smtpd_delay_reject = yes" (which is the default) and use:
</p>

<blockquote>
<pre>
smtpd_client_restrictions = permit_sasl_authenticated, reject
</pre>
</blockquote>

<p>
See the SASL_README file for SASL configuration and operation details.
</p>

%PARAM smtpd_sasl_authenticated_header no

<p> Report the SASL authenticated user name in the smtpd(8) Received
message header.  </p>

<p> This feature is available in Postfix 2.3 and later.  </p>

%PARAM smtpd_sasl_exceptions_networks

<p>
What remote SMTP clients the Postfix SMTP server will not offer
AUTH support to.
</p>

<p>
Some clients (Netscape 4 at least) have a bug that causes them to
require a login and password whenever AUTH is offered, whether it's
necessary or not. To work around this, specify, for example,
$mynetworks to prevent Postfix from offering AUTH to local clients.
</p>

<p>
Specify a list of network/netmask patterns, separated by commas
and/or whitespace. The mask specifies the number of bits in the
network part of a host address. You can also "/file/name" or
"type:table" patterns.  A "/file/name" pattern is replaced by its
contents; a "type:table" lookup table is matched when a table entry
matches a lookup string (the lookup result is ignored).  Continue
long lines by starting the next line with whitespace. Specify
"!pattern" to exclude an address or network block from the list.
The form "!/file/name" is supported only in Postfix version 2.4 and
later.  </p>

<p> Note: IP version 6 address information must be specified inside
<tt>[]</tt> in the smtpd_sasl_exceptions_networks value, and in
files specified with "/file/name".  IP version 6 addresses contain
the ":" character, and would otherwise be confused with a "type:table"
pattern.  </p>

<p>
Example:
</p>

<pre>
smtpd_sasl_exceptions_networks = $mynetworks
</pre>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtpd_sasl_local_domain

<p>
The name of the Postfix SMTP server's local SASL authentication
realm.
</p>

<p>
By default, the local authentication realm name is the null string.
</p>

<p>
Examples:
</p>

<pre>
smtpd_sasl_local_domain = $mydomain
smtpd_sasl_local_domain = $myhostname
</pre>

%PARAM smtpd_sasl_security_options noanonymous

<p> Postfix SMTP server SASL security options; as of Postfix 2.3
the list of available
features depends on the SASL server implementation that is selected
with <b>smtpd_sasl_type</b>.  </p>

<p> The following security features are defined for the <b>cyrus</b>
server SASL implementation: </p>

<p>
Restrict what authentication mechanisms the Postfix SMTP server
will offer to the client.  The list of available authentication
mechanisms is system dependent.
</p>

<p>
Specify zero or more of the following:
</p>

<dl>

<dt><b>noplaintext</b></dt>

<dd>Disallow methods that use plaintext passwords. </dd>

<dt><b>noactive</b></dt>

<dd>Disallow methods subject to active (non-dictionary) attack. </dd>

<dt><b>nodictionary</b></dt>

<dd>Disallow methods subject to passive (dictionary) attack. </dd>

<dt><b>noanonymous</b></dt>

<dd>Disallow methods that allow anonymous authentication. </dd>

<dt><b>forward_secrecy</b></dt>

<dd>Only allow methods that support forward secrecy (Dovecot only).
</dd>

<dt><b>mutual_auth</b></dt>

<dd>Only allow methods that provide mutual authentication (not available
with Cyrus SASL version 1). </dd>

</dl>

<p>
By default, the Postfix SMTP server accepts plaintext passwords but
not anonymous logins.
</p>

<p>
Warning: it appears that clients try authentication methods in the
order as advertised by the server (e.g., PLAIN ANONYMOUS CRAM-MD5)
which means that if you disable plaintext passwords, clients will
log in anonymously, even when they should be able to use CRAM-MD5.
So, if you disable plaintext logins, disable anonymous logins too.
Postfix treats anonymous login as no authentication.
</p>

<p>
Example:
</p>

<pre>
smtpd_sasl_security_options = noanonymous, noplaintext
</pre>

%PARAM smtpd_sender_login_maps

<p>
Optional lookup table with the SASL login names that own sender
(MAIL FROM) addresses.
</p>

<p>
Specify zero or more "type:table" lookup tables. With lookups from
indexed files such as DB or DBM, or from networked tables such as
NIS, LDAP or SQL, the following search operations are done with a
sender address of <i>user@domain</i>:  </p>

<dl>

<dt> 1) <i>user@domain</i> </dt>

<dd>This table lookup is always done and has the highest precedence. </dd>

<dt> 2) <i>user</i> </dt>

<dd>This table lookup is done only when the <i>domain</i> part of the
sender address matches $myorigin, $mydestination, $inet_interfaces
or $proxy_interfaces. </dd>

<dt> 3) <i>@domain</i> </dt>

<dd>This table lookup is done last and has the lowest precedence. </dd>

</dl>

<p>
In all cases the result of table lookup must be either "not found"
or a list of SASL login names separated by comma and/or whitespace.
</p>

%PARAM smtpd_sender_restrictions

<p>
Optional restrictions that the Postfix SMTP server applies in the
context of the MAIL FROM command.
See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
restriction lists" for a discussion of evaluation context and time.
</p>

<p>
The default is to permit everything.
</p>

<p>
Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.
</p>

<p>
The following restrictions are specific to the sender address
received with the MAIL FROM command.
</p>

<dl>

<dt><b><a name="check_sender_access">check_sender_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the MAIL FROM
address, domain, parent domains, or localpart@, and execute the
corresponding action. </dd>

<dt><b><a name="check_sender_mx_access">check_sender_mx_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the MX hosts for
the MAIL FROM address, and execute the corresponding action.  Note:
a result of "OK" is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from blacklists.  This
feature is available in Postfix 2.1 and later. </dd>

<dt><b><a name="check_sender_ns_access">check_sender_ns_access</a> <i><a href="DATABASE_README.html">type:table</a></i></b></dt>

<dd>Search the specified access(5) database for the DNS servers
for the MAIL FROM address, and execute the corresponding action.
Note: a result of "OK" is not allowed for safety reasons. Instead,
use DUNNO in order to exclude specific hosts from blacklists.  This
feature is available in Postfix 2.1 and later.  </dd>

<dt><b><a name="reject_authenticated_sender_login_mismatch">reject_authenticated_sender_login_mismatch</a></b></dt>

<dd>Enforces the reject_sender_login_mismatch restriction for
authenticated clients only. This feature is available in
Postfix version 2.1 and later. </dd>

<dt><b><a name="reject_non_fqdn_sender">reject_non_fqdn_sender</a></b></dt>

<dd>Reject the request when the MAIL FROM address is not in
fully-qualified domain form, as required by the RFC. <br> The
non_fqdn_reject_code parameter specifies the response code for
rejected requests (default: 504). </dd>

<dt><b><a name="reject_rhsbl_sender">reject_rhsbl_sender <i>rbl_domain=d.d.d.d</i></a></b></dt>

<dd>Reject the request when the MAIL FROM domain is listed with
the A record "<i>d.d.d.d</i>" under <i>rbl_domain</i> (Postfix
version 2.1 and later only).  If no "<i>=d.d.d.d</i>" is specified,
reject the request when the MAIL FROM domain is
listed with any A record under <i>rbl_domain</i>. <br> The
maps_rbl_reject_code parameter specifies the response code for
rejected requests (default:  554); the default_rbl_reply parameter
specifies the default server reply; and the rbl_reply_maps parameter
specifies tables with server replies indexed by <i>rbl_domain</i>.
This feature is available in Postfix 2.0 and later.</dd>

<dt><b><a name="reject_sender_login_mismatch">reject_sender_login_mismatch</a></b></dt>

<dd>Reject the request when $smtpd_sender_login_maps specifies an
owner for the MAIL FROM address, but the client is not (SASL) logged
in as that MAIL FROM address owner; or when the client is (SASL)
logged in, but the client login name doesn't own the MAIL FROM
address according to $smtpd_sender_login_maps.</dd>

<dt><b><a name="reject_unauthenticated_sender_login_mismatch">reject_unauthenticated_sender_login_mismatch</a></b></dt>

<dd>Enforces the reject_sender_login_mismatch restriction for
unauthenticated clients only. This feature is available in
Postfix version 2.1 and later. </dd>

<dt><b><a name="reject_unknown_sender_domain">reject_unknown_sender_domain</a></b></dt>

<dd>Reject the request when Postfix is not final destination for
the sender address, and the MAIL FROM address has no DNS A or MX
record, or when it has a malformed MX record such as a record with
a zero-length MX hostname (Postfix version 2.3 and later). <br> The
unknown_address_reject_code parameter specifies the numerical
response code for rejected requests (default: 450).  The response
is always 450 in case of a temporary DNS error. <br> The
unknown_address_tempfail_action parameter specifies the action
after a temporary DNS error (default: defer_if_permit). </dd>

<dt><b><a name="reject_unlisted_sender">reject_unlisted_sender</a></b></dt>

<dd>Reject the request when the MAIL FROM address is not listed in
the list of valid recipients for its domain class. See the
smtpd_reject_unlisted_sender parameter description for details.
This feature is available in Postfix 2.1 and later.</dd>

<dt><b><a name="reject_unverified_sender">reject_unverified_sender</a></b></dt>

<dd>Reject the request when mail to the MAIL FROM address is known to
bounce, or when the sender address destination is not reachable.
Address verification information is managed by the verify(8) server;
see the ADDRESS_VERIFICATION_README file for details. <br> The
unverified_sender_reject_code parameter specifies the numerical
response code when an address is known to bounce (default: 450,
change into 550 when you are confident that it is safe to do so).
<br>The unverified_sender_defer_code specifies the numerical response
code when an address address probe failed due to a temporary problem
(default: 450).  <br> The unverified_sender_tempfail_action parameter
specifies the action after address probe failure due to a temporary
problem (default: defer_if_permit).  <br> This feature is available
in Postfix 2.1 and later.  </dd>

</dl>

<p>
Other restrictions that are valid in this context:
</p>

<ul>

<li> <a href="#generic">Generic</a> restrictions that can be used
in any SMTP command context, described under smtpd_client_restrictions.

<li> SMTP command specific restrictions described under
smtpd_client_restrictions and smtpd_helo_restrictions.

<li> SMTP command specific restrictions described under
smtpd_recipient_restrictions. When recipient restrictions are listed
under smtpd_sender_restrictions, they have effect only with
"smtpd_delay_reject = yes", so that $smtpd_sender_restrictions is
evaluated at the time of the RCPT TO command.

</ul>

<p>
Examples:
</p>

<pre>
smtpd_sender_restrictions = reject_unknown_sender_domain
smtpd_sender_restrictions = reject_unknown_sender_domain,
    check_sender_access hash:/etc/postfix/access
</pre>

%PARAM smtpd_timeout normal: 300s, stress: 10s

<p>
The time limit for sending a Postfix SMTP server response and for
receiving a remote SMTP client request. Normally the default limit
is 300s, but it changes under overload to just 10s with Postfix 2.6
and later.
</p>

<p>
Note: if you set SMTP time limits to very large values you may have
to update the global ipc_timeout parameter.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM soft_bounce no

<p>
Safety net to keep mail queued that would otherwise be returned to
the sender.  This parameter disables locally-generated bounces,
and prevents the Postfix SMTP server from rejecting mail permanently,
by changing 5xx reply codes into 4xx.  However, soft_bounce is no
cure for address rewriting mistakes or mail routing mistakes.
</p>

<p>
Example:
</p>

<pre>
soft_bounce = yes
</pre>

%PARAM stale_lock_time 500s

<p>
The time after which a stale exclusive mailbox lockfile is removed.
This is used for delivery to file or mailbox.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM strict_rfc821_envelopes no

<p>
Require that addresses received in SMTP MAIL FROM and RCPT TO
commands are enclosed with &lt;&gt;, and that those addresses do
not contain RFC 822 style comments or phrases.  This stops mail
from poorly written software.
</p>

<p>
By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL
FROM and RCPT TO addresses.
</p>

%PARAM swap_bangpath yes

<p>
Enable the rewriting of "site!user" into "user@site".  This is
necessary if your machine is connected to UUCP networks.  It is
enabled by default.
</p>

<p> Note: with Postfix version 2.2, message header address rewriting
happens only when one of the following conditions is true: </p>

<ul>

<li> The message is received with the Postfix sendmail(1) command,

<li> The message is received from a network client that matches
$local_header_rewrite_clients,

<li> The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty value.

</ul>

<p> To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all". </p>

<p>
Example:
</p>

<pre>
swap_bangpath = no
</pre>

%PARAM syslog_facility mail

<p>
The syslog facility of Postfix logging. Specify a facility as
defined in syslog.conf(5). The default facility is "mail".
</p>

<p>
Warning: a non-default syslog_facility setting takes effect only
after a Postfix process has completed initialization.  Errors during
process initialization will be logged with the default facility.
Examples are errors while parsing the command line arguments, and
errors while accessing the Postfix main.cf configuration file.
</p>

%PARAM syslog_name see "postconf -d" output

<p>
The mail system name that is prepended to the process name in syslog
records, so that "smtpd" becomes, for example, "postfix/smtpd".
</p>

<p>
Warning: a non-default syslog_name setting takes effect only after
a Postfix process has completed initialization. Errors during
process initialization will be logged with the default name. Examples
are errors while parsing the command line arguments, and errors
while accessing the Postfix main.cf configuration file.
</p>

%PARAM transport_maps

<p>
Optional lookup tables with mappings from recipient address to
(message delivery transport, next-hop destination).  See transport(5)
for details.
</p>

<p>
Specify zero or more "type:table" lookup tables.  If you use this
feature with local files, run "<b>postmap /etc/postfix/transport</b>"
after making a change.  </p>

<p> For safety reasons, as of Postfix 2.3 this feature does not
allow $number substitutions in regular expression maps. </p>

<p>
Examples:
</p>

<pre>
transport_maps = dbm:/etc/postfix/transport
transport_maps = hash:/etc/postfix/transport
</pre>

%PARAM transport_retry_time 60s

<p>
The time between attempts by the Postfix queue manager to contact
a malfunctioning message delivery transport.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM trigger_timeout 10s

<p>
The time limit for sending a trigger to a Postfix daemon (for
example, the pickup(8) or qmgr(8) daemon). This time limit prevents
programs from getting stuck when the mail system is under heavy
load.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM unknown_address_reject_code 450

<p>
The numerical Postfix SMTP server response code when a sender or
recipient address is rejected by the reject_unknown_sender_domain
or reject_unknown_recipient_domain restriction.  The response is
always 450 in case of a temporary DNS error.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

%PARAM unknown_client_reject_code 450

<p>
The numerical Postfix SMTP server response code when a client
without valid address &lt;=&gt; name mapping is rejected by the
reject_unknown_client_hostname restriction. The SMTP server always replies
with 450 when the mapping failed due to a temporary error condition.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

%PARAM unknown_hostname_reject_code 450

<p>
The numerical Postfix SMTP server response code when the hostname
specified with the HELO or EHLO command is rejected by the
reject_unknown_helo_hostname restriction.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

%PARAM unknown_local_recipient_reject_code 550

<p>
The numerical Postfix SMTP server response code when a recipient
address is local, and $local_recipient_maps specifies a list of
lookup tables that does not match the recipient.  A recipient
address is local when its domain matches $mydestination,
$proxy_interfaces or $inet_interfaces.
</p>

<p>
The default setting is 550 (reject mail) but it is safer to initially
use 450 (try again later) so you have time to find out if your
local_recipient_maps settings are OK.
</p>

<p>
Example:
</p>

<pre>
unknown_local_recipient_reject_code = 450
</pre>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM unverified_recipient_reject_code 450

<p>
The numerical Postfix SMTP server response when a recipient address
is rejected by the reject_unverified_recipient restriction.
</p>

<p>
Unlike elsewhere in Postfix, you can specify 250 in order to
accept the address anyway.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM unverified_recipient_defer_code 450

<p>
The numerical Postfix SMTP server response when a recipient address
probe fails due to a temporary error condition.
</p>

<p>
Unlike elsewhere in Postfix, you can specify 250 in order to
accept the address anyway.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

<p>
This feature is available in Postfix 2.6 and later.
</p>

%PARAM unverified_sender_reject_code 450

<p>
The numerical Postfix SMTP server response code when a recipient
address is rejected by the reject_unverified_sender restriction.
</p>

<p>
Unlike elsewhere in Postfix, you can specify 250 in order to
accept the address anyway.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM unverified_sender_defer_code 450

<p>
The numerical Postfix SMTP server response code when a sender address
probe fails due to a temporary error condition.
</p>

<p>
Unlike elsewhere in Postfix, you can specify 250 in order to
accept the address anyway.
</p>

<p>
Do not change this unless you have a complete understanding of RFC 2821.
</p>

<p>
This feature is available in Postfix 2.6 and later.
</p>

%PARAM virtual_alias_domains $virtual_alias_maps

<p> Postfix is final destination for the specified list of virtual
alias domains, that is, domains for which all addresses are aliased
to addresses in other local or remote domains. The SMTP server
validates recipient addresses with $virtual_alias_maps and rejects
non-existent recipients. See also the virtual alias domain class
in the ADDRESS_CLASS_README file </p>

<p>
This feature is available in Postfix 2.0 and later. The default
value is backwards compatible with Postfix version 1.1.
</p>

<p>
The default value is $virtual_alias_maps so that you can keep all
information about virtual alias domains in one place.  If you have
many users, it is better to separate information that changes more
frequently (virtual address -&gt; local or remote address mapping)
from information that changes less frequently (the list of virtual
domain names).
</p>

<p> Specify a list of host or domain names, "/file/name" or
"type:table" patterns, separated by commas and/or whitespace. A
"/file/name" pattern is replaced by its contents; a "type:table"
lookup table is matched when a table entry matches a lookup string
(the lookup result is ignored).  Continue long lines by starting
the next line with whitespace. Specify "!pattern" to exclude a host
or domain name from the list. The form "!/file/name" is supported
only in Postfix version 2.4 and later.  </p>

<p>
See also the VIRTUAL_README and ADDRESS_CLASS_README documents
for further information.
</p>

<p>
Example:
</p>

<pre>
virtual_alias_domains = virtual1.tld virtual2.tld
</pre>

%PARAM virtual_alias_expansion_limit 1000

<p>
The maximal number of addresses that virtual alias expansion produces
from each original recipient.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM virtual_alias_maps $virtual_maps

<p>
Optional lookup tables that alias specific mail addresses or domains
to other local or remote address.  The table format and lookups
are documented in virtual(5). For an overview of Postfix address
manipulations see the ADDRESS_REWRITING_README document.
</p>

<p>
This feature is available in Postfix 2.0 and later. The default
value is backwards compatible with Postfix version 1.1.
</p>

<p>
If you use this feature with indexed files, run "<b>postmap
/etc/postfix/virtual</b>" after changing the file.
</p>

<p>
Examples:
</p>

<pre>
virtual_alias_maps = dbm:/etc/postfix/virtual
virtual_alias_maps = hash:/etc/postfix/virtual
</pre>

%PARAM virtual_alias_recursion_limit 1000

<p>
The maximal nesting depth of virtual alias expansion.  Currently
the recursion limit is applied only to the left branch of the
expansion graph, so the depth of the tree can in the worst case
reach the sum of the expansion and recursion limits.  This may
change in the future.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%CLASS trouble-shooting Trouble shooting

<p>
The DEBUG_README document describes how to debug parts of the
Postfix mail system. The methods vary from making the software log
a lot of detail, to running some daemon processes under control of
a call tracer or debugger.
</p>

%PARAM debugger_command

<p>
The external command to execute when a Postfix daemon program is
invoked with the -D option.
</p>

<p>
Use "command .. &amp; sleep 5" so that the debugger can attach before
the process marches on. If you use an X-based debugger, be sure to
set up your XAUTHORITY environment variable before starting Postfix.
</p>

<p>
Example:
</p>

<pre>
debugger_command =
    PATH=/usr/bin:/usr/X11R6/bin
    ddd $daemon_directory/$process_name $process_id &amp; sleep 5
</pre>

%PARAM 2bounce_notice_recipient postmaster

<p> The recipient of undeliverable mail that cannot be returned to
the sender.  This feature is enabled with the notify_classes
parameter.  </p>

%PARAM address_verify_service_name verify

<p>
The name of the verify(8) address verification service. This service
maintains the status of sender and/or recipient address verification
probes, and generates probes on request by other Postfix processes.
</p>

%PARAM alternate_config_directories

<p>
A list of non-default Postfix configuration directories that may
be specified with "-c config_directory" on the command line, or
via the MAIL_CONFIG environment parameter.
</p>

<p>
This list must be specified in the default Postfix configuration
directory, and is used by set-gid Postfix commands such as postqueue(1)
and postdrop(1).
</p>

%PARAM append_at_myorigin yes

<p>
With locally submitted mail, append the string "@$myorigin" to mail
addresses without domain information. With remotely submitted mail,
append the string "@$remote_header_rewrite_domain" instead.
</p>

<p>
Note 1: this feature is enabled by default and must not be turned off.
Postfix does not support domain-less addresses.
</p>

<p> Note 2: with Postfix version 2.2, message header address rewriting
happens only when one of the following conditions is true: </p>

<ul>

<li> The message is received with the Postfix sendmail(1) command,

<li> The message is received from a network client that matches
$local_header_rewrite_clients,

<li> The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty value.

</ul>

<p> To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all". </p>

%PARAM append_dot_mydomain yes

<p>
With locally submitted mail, append the string ".$mydomain" to
addresses that have no ".domain" information. With remotely submitted
mail, append the string ".$remote_header_rewrite_domain"
instead.
</p>

<p>
Note 1: this feature is enabled by default. If disabled, users will not be
able to send mail to "user@partialdomainname" but will have to
specify full domain names instead.
</p>

<p> Note 2: with Postfix version 2.2, message header address rewriting
happens only when one of the following conditions is true: </p>

<ul>

<li> The message is received with the Postfix sendmail(1) command,

<li> The message is received from a network client that matches
$local_header_rewrite_clients,

<li> The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty value.

</ul>

<p> To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all". </p>

%PARAM application_event_drain_time 100s

<p>
How long the postkick(1) command waits for a request to enter the
server's input buffer before giving up.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM authorized_flush_users static:anyone

<p>
List of users who are authorized to flush the queue.
</p>

<p>
By default, all users are allowed to flush the queue.  Access is
always granted if the invoking user is the super-user or the
$mail_owner user.  Otherwise, the real UID of the process is looked
up in the system password file, and access is granted only if the
corresponding login name is on the access list.  The username
"unknown" is used for processes whose real UID is not found in the
password file.  </p>

<p>
Specify a list of user names, "/file/name" or "type:table" patterns,
separated by commas and/or whitespace. The list is matched left to
right, and the search stops on the first match. A "/file/name"
pattern is replaced
by its contents; a "type:table" lookup table is matched when a name
matches a lookup key (the lookup result is ignored).  Continue long
lines by starting the next line with whitespace. Specify "!pattern"
to exclude a name from the list. The form "!/file/name" is supported
only in Postfix version 2.4 and later.  </p>

<p>
This feature is available in Postfix 2.2 and later.
</p>

%PARAM authorized_mailq_users static:anyone

<p>
List of users who are authorized to view the queue.
</p>

<p>
By default, all users are allowed to view the queue.  Access is
always granted if the invoking user is the super-user or the
$mail_owner user.  Otherwise, the real UID of the process is looked
up in the system password file, and access is granted only if the
corresponding login name is on the access list.  The username
"unknown" is used for processes whose real UID is not found in the
password file.  </p>

<p>
Specify a list of user names, "/file/name" or "type:table" patterns,
separated by commas and/or whitespace. The list is matched left to
right, and the search stops on the first match. A "/file/name"
pattern is replaced
by its contents; a "type:table" lookup table is matched when a name
matches a lookup key (the lookup result is ignored).  Continue long
lines by starting the next line with whitespace. Specify "!pattern"
to exclude a user name from the list. The form "!/file/name" is
supported only in Postfix version 2.4 and later.  </p>

<p>
This feature is available in Postfix 2.2 and later.
</p>

%PARAM authorized_submit_users static:anyone

<p>
List of users who are authorized to submit mail with the sendmail(1)
command (and with the privileged postdrop(1) helper command).
</p>

<p>
By default, all users are allowed to submit mail.  Otherwise, the
real UID of the process is looked up in the system password file,
and access is granted only if the corresponding login name is on
the access list.  The username "unknown" is used for processes
whose real UID is not found in the password file. To deny mail
submission access to all users specify an empty list.  </p>

<p>
Specify a list of user names, "/file/name" or "type:table" patterns,
separated by commas and/or whitespace. The list is matched left to right,
and the search stops on the first match. A "/file/name" pattern is
replaced by its contents;
a "type:table" lookup table is matched when a name matches a lookup key
(the lookup result is ignored).  Continue long lines by starting the
next line with whitespace. Specify "!pattern" to exclude a user
name from the list. The form "!/file/name" is supported only in
Postfix version 2.4 and later.  </p>

<p>
Example:
</p>

<pre>
authorized_submit_users = !www, static:all
</pre>

<p>
This feature is available in Postfix 2.2 and later.
</p>

%PARAM backwards_bounce_logfile_compatibility yes

<p>
Produce additional bounce(8) logfile records that can be read by
Postfix versions before 2.0. The current and more extensible "name =
value" format is needed in order to implement more sophisticated
functionality.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM bounce_notice_recipient postmaster

<p>
The recipient of postmaster notifications with the message headers
of mail that Postfix did not deliver and of SMTP conversation
transcripts of mail that Postfix did not receive.  This feature is
enabled with the notify_classes parameter.  </p>

%PARAM bounce_service_name bounce

<p>
The name of the bounce(8) service. This service maintains a record
of failed delivery attempts and generates non-delivery notifications.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM broken_sasl_auth_clients no

<p>
Enable inter-operability with SMTP clients that implement an obsolete
version of the AUTH command (RFC 4954). Examples of such clients
are MicroSoft Outlook Express version 4 and MicroSoft Exchange
version 5.0.
</p>

<p>
Specify "broken_sasl_auth_clients = yes" to have Postfix advertise
AUTH support in a non-standard way.
</p>

%PARAM cleanup_service_name cleanup

<p>
The name of the cleanup(8) service. This service rewrites addresses
into the standard form, and performs canonical(5) address mapping
and virtual(5) aliasing.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM anvil_status_update_time 600s

<p>
How frequently the anvil(8) connection and rate limiting server
logs peak usage information.
</p>

<p>
This feature is available in Postfix 2.2 and later.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM enable_errors_to no

<p> Report mail delivery errors to the address specified with the
non-standard Errors-To: message header, instead of the envelope
sender address (this feature is removed with Postfix version 2.2, is
turned off by default with Postfix version 2.1, and is always turned on
with older Postfix versions).  </p>

%PARAM extract_recipient_limit 10240

<p>
The maximal number of recipient addresses that Postfix will extract
from message headers when mail is submitted with "<b>sendmail -t</b>".
</p>

<p>
This feature was removed in Postfix version 2.1.
</p>

%PARAM anvil_rate_time_unit 60s

<p>
The time unit over which client connection rates and other rates
are calculated.
</p>

<p>
This feature is implemented by the anvil(8) service which is available
in Postfix version 2.2 and later.
</p>

<p>
The default interval is relatively short. Because of the high
frequency of updates, the anvil(8) server uses volatile memory
only. Thus, information is lost whenever the process terminates.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM command_expansion_filter see "postconf -d" output

<p>
Restrict the characters that the local(8) delivery agent allows in
$name expansions of $mailbox_command and $command_execution_directory.
Characters outside the
allowed set are replaced by underscores.
</p>

%PARAM content_filter

<p> After the message is queued, send the entire message to the
specified <i>transport:destination</i>. The <i>transport</i> name
specifies the first field of a mail delivery agent definition in
master.cf; the syntax of the next-hop <i>destination</i> is described
in the manual page of the corresponding delivery agent.  More
information about external content filters is in the Postfix
FILTER_README file.  </p>

<p> Notes: </p>

<ul>

<li> <p> This setting has lower precedence than a FILTER action
that is specified in an access(5), header_checks(5) or body_checks(5)
table. </p>

<li> <p> The meaning of an empty next-hop filter <i>destination</i>
is version dependent.  Postfix 2.7 and later will use the recipient
domain; earlier versions will use $myhostname.  Specify
"default_filter_nexthop = $myhostname" for compatibility with Postfix
2.6 or earlier, or specify a content_filter value with an explicit
next-hop <i>destination</i>.  </p>

</ul>

%PARAM default_delivery_slot_discount 50

<p>
The default value for transport-specific _delivery_slot_discount
settings.
</p>

<p>
This parameter speeds up the moment when a message preemption can
happen. Instead of waiting until the full amount of delivery slots
required is available, the preemption can happen when
transport_delivery_slot_discount percent of the required amount
plus transport_delivery_slot_loan still remains to be accumulated.
Note that the full amount will still have to be accumulated before
another preemption can take place later.
</p>

<p> Use <i>transport</i>_delivery_slot_discount to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

%PARAM default_delivery_slot_loan 3

<p>
The default value for transport-specific _delivery_slot_loan
settings.
</p>

<p>
This parameter speeds up the moment when a message preemption can
happen. Instead of waiting until the full amount of delivery slots
required is available, the preemption can happen when
transport_delivery_slot_discount percent of the required amount
plus transport_delivery_slot_loan still remains to be accumulated.
Note that the full amount will still have to be accumulated before
another preemption can take place later.
</p>

<p> Use <i>transport</i>_delivery_slot_loan to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

%CLASS verp VERP Support

<p>
With VERP style delivery, each recipient of a message receives a
customized copy of the message with his/her own recipient address
encoded in the envelope sender address.  The VERP_README file
describes configuration and operation details of Postfix support
for variable envelope return path addresses.  VERP style delivery
is requested with the SMTP XVERP command or with the "<b>sendmail
-V</b>" command-line option and is available in Postfix
1.1 and later.
</p>

%PARAM default_verp_delimiters +=

<p> The two default VERP delimiter characters. These are used when
no explicit delimiters are specified with the SMTP XVERP command
or with the "<b>sendmail -V</b>" command-line option. Specify
characters that are allowed by the verp_delimiter_filter setting.
</p>

<p>
This feature is available in Postfix 1.1 and later.
</p>

%PARAM defer_service_name defer

<p>
The name of the defer service. This service is implemented by the
bounce(8) daemon and maintains a record
of failed delivery attempts and generates non-delivery notifications.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM delay_notice_recipient postmaster

<p>
The recipient of postmaster notifications with the message headers
of mail that cannot be delivered within $delay_warning_time time
units.  </p>

<p>
This feature is enabled with the delay_warning_time parameter.
</p>

%PARAM delay_warning_time 0h

<p>
The time after which the sender receives the message headers of
mail that is still queued.
</p>

<p>
To enable this feature, specify a non-zero time value (an integral
value plus an optional one-letter suffix that specifies the time
unit).
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is h (hours).
</p>

%PARAM disable_dns_lookups no

<p>
Disable DNS lookups in the Postfix SMTP and LMTP clients. When
disabled, hosts are looked up with the getaddrinfo() system
library routine which normally also looks in /etc/hosts.
</p>

<p>
DNS lookups are enabled by default.
</p>

%CLASS mime MIME Processing

<p>
MIME processing is available in Postfix as of version 2.0.  Older
Postfix versions do not recognize MIME headers inside the message
body.
</p>

%PARAM disable_mime_input_processing no

<p>
Turn off MIME processing while receiving mail. This means that no
special treatment is given to Content-Type: message headers, and
that all text after the initial message headers is considered to
be part of the message body.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

<p>
Mime input processing is enabled by default, and is needed in order
to recognize MIME headers in message content.
</p>

%PARAM disable_mime_output_conversion no

<p>
Disable the conversion of 8BITMIME format to 7BIT format.  Mime
output conversion is needed when the destination does not advertise
8BITMIME support.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM disable_verp_bounces no

<p>
Disable sending one bounce report per recipient.
</p>

<p>
The default, one per recipient, is what ezmlm needs.
</p>

<p>
This feature is available in Postfix 1.1 and later.
</p>

%PARAM dont_remove 0

<p>
Don't remove queue files and save them to the "saved" mail queue.
This is a debugging aid.  To inspect the envelope information and
content of a Postfix queue file, use the postcat(1) command.
</p>

%PARAM empty_address_recipient MAILER-DAEMON

<p>
The recipient of mail addressed to the null address.  Postfix does
not accept such addresses in SMTP commands, but they may still be
created locally as the result of configuration or software error.
</p>

%PARAM error_notice_recipient postmaster

<p> The recipient of postmaster notifications about mail delivery
problems that are caused by policy, resource, software or protocol
errors.  These notifications are enabled with the notify_classes
parameter.  </p>

%PARAM error_service_name error

<p>
The name of the error(8) pseudo delivery agent. This service always
returns mail as undeliverable.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM expand_owner_alias no

<p>
When delivering to an alias "aliasname" that has an "owner-aliasname"
companion alias, set the envelope sender address to the expansion
of the "owner-aliasname" alias. Normally, Postfix sets the envelope
sender address to the name of the "owner-aliasname" alias.
</p>

%PARAM fallback_transport

<p>
Optional message delivery transport that the local(8) delivery
agent should use for names that are not found in the aliases(5)
or UNIX password database.
</p>

<p> The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.  </p>

%PARAM fault_injection_code 0

<p>
Force specific internal tests to fail, to test the handling of
errors that are difficult to reproduce otherwise.
</p>

%PARAM flush_service_name flush

<p>
The name of the flush(8) service. This service maintains per-destination
logfiles with the queue file names of mail that is queued for those
destinations.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM forward_expansion_filter see "postconf -d" output

<p>
Restrict the characters that the local(8) delivery agent allows in
$name expansions of $forward_path.  Characters outside the
allowed set are replaced by underscores.
</p>

%PARAM header_address_token_limit 10240

<p>
The maximal number of address tokens are allowed in an address
message header. Information that exceeds the limit is discarded.
The limit is enforced by the cleanup(8) server.
</p>

%PARAM helpful_warnings yes

<p>
Log warnings about problematic configuration settings, and provide
helpful suggestions.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM lmtp_cache_connection yes

<p>
Keep Postfix LMTP client connections open for up to $max_idle
seconds. When the LMTP client receives a request for the same
connection the connection is reused.
</p>

<p> This parameter is available in Postfix version 2.2 and earlier.
With Postfix version 2.3 and later, see lmtp_connection_cache_on_demand,
lmtp_connection_cache_destinations, or lmtp_connection_reuse_time_limit.
</p>

<p>
The effectiveness of cached connections will be determined by the
number of LMTP servers in use, and the concurrency limit specified
for the LMTP client. Cached connections are closed under any of
the following conditions:
</p>

<ul>

<li> The LMTP client idle time limit is reached.  This limit is
specified with the Postfix max_idle configuration parameter.

<li> A delivery request specifies a different destination than the
one currently cached.

<li> The per-process limit on the number of delivery requests is
reached.  This limit is specified with the Postfix max_use
configuration parameter.

<li> Upon the onset of another delivery request, the LMTP server
associated with the current session does not respond to the RSET
command.

</ul>

<p>
Most of these limitations will be removed after Postfix implements
a connection cache that is shared among multiple LMTP client
programs.
</p>

%PARAM lmtp_sasl_auth_enable no

<p>
Enable SASL authentication in the Postfix LMTP client.
</p>

%PARAM lmtp_sasl_password_maps

<p>
Optional LMTP client lookup tables with one username:password entry
per host or domain.  If a remote host or domain has no username:password
entry, then the Postfix LMTP client will not attempt to authenticate
to the remote host.
</p>

%PARAM lmtp_sasl_security_options noplaintext, noanonymous

<p> SASL security options; as of Postfix 2.3 the list of available
features depends on the SASL client implementation that is selected
with <b>lmtp_sasl_type</b>.  </p>

<p> The following security features are defined for the <b>cyrus</b>
client SASL implementation: </p>

<dl>

<dt><b>noplaintext</b></dt>

<dd>Disallow authentication methods that use plaintext passwords. </dd>

<dt><b>noactive</b></dt>

<dd>Disallow authentication methods that are vulnerable to non-dictionary
active attacks. </dd>

<dt><b>nodictionary</b></dt>

<dd>Disallow authentication methods that are vulnerable to passive
dictionary attack. </dd>

<dt><b>noanonymous</b></dt>

<dd>Disallow anonymous logins. </dd>

</dl>

<p>
Example:
</p>

<pre>
lmtp_sasl_security_options = noplaintext
</pre>

%PARAM lmtp_tcp_port 24

<p>
The default TCP port that the Postfix LMTP client connects to.
</p>

%PARAM mail_release_date see "postconf -d" output

<p>
The Postfix release date, in "YYYYMMDD" format.
</p>

%PARAM mailbox_command_maps

<p>
Optional lookup tables with per-recipient external commands to use
for local(8) mailbox delivery.  Behavior is as with mailbox_command.
</p>

<p> The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.  </p>

%PARAM mailbox_delivery_lock see "postconf -d" output

<p>
How to lock a UNIX-style local(8) mailbox before attempting delivery.
For a list of available file locking methods, use the "<b>postconf
-l</b>" command.
</p>

<p>
This setting is ignored with <b>maildir</b> style delivery,
because such deliveries are safe without explicit locks.
</p>

<p>
Note: The <b>dotlock</b> method requires that the recipient UID or
GID has write access to the parent directory of the mailbox file.
</p>

<p>
Note: the default setting of this parameter is system dependent.
</p>

%PARAM mailbox_transport

<p>
Optional message delivery transport that the local(8) delivery
agent should use for mailbox delivery to all local recipients,
whether or not they are found in the UNIX passwd database.
</p>

<p> The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.  </p>

%PARAM mailq_path see "postconf -d" output

<p>
Sendmail compatibility feature that specifies where the Postfix
mailq(1) command is installed. This command can be used to
list the Postfix mail queue.
</p>

%PARAM manpage_directory see "postconf -d" output

<p>
Where the Postfix manual pages are installed.
</p>

%PARAM maps_rbl_domains

<p>
Obsolete feature: use the reject_rbl_client feature instead.
</p>

%PARAM mime_boundary_length_limit 2048

<p>
The maximal length of MIME multipart boundary strings. The MIME
processor is unable to distinguish between boundary strings that
do not differ in the first $mime_boundary_length_limit characters.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM mime_header_checks $header_checks

<p>
Optional lookup tables for content inspection of MIME related
message headers, as described in the header_checks(5) manual page.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM mime_nesting_limit 100

<p>
The maximal recursion level that the MIME processor will handle.
Postfix refuses mail that is nested deeper than the specified limit.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM mynetworks_style subnet

<p>
The method to generate the default value for the mynetworks parameter.
This is the list of trusted networks for relay access control etc.
</p>

<ul>

<li><p>Specify "mynetworks_style = host" when Postfix should
"trust" only the local machine. </p>

<li><p>Specify "mynetworks_style = subnet" when Postfix
should "trust" SMTP clients in the same IP subnetworks as the local
machine.  On Linux, this works correctly only with interfaces
specified with the "ifconfig" command. </p>

<li><p>Specify "mynetworks_style = class" when Postfix should
"trust" SMTP clients in the same IP class A/B/C networks as the
local machine.  Don't do this with a dialup site - it would cause
Postfix to "trust" your entire provider's network.  Instead, specify
an explicit mynetworks list by hand, as described with the mynetworks
configuration parameter. </p>

</ul>

%PARAM nested_header_checks $header_checks

<p>
Optional lookup tables for content inspection of non-MIME message
headers in attached messages, as described in the header_checks(5)
manual page.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM newaliases_path see "postconf -d" output

<p>
Sendmail compatibility feature that specifies the location of the
newaliases(1) command. This command can be used to rebuild the
local(8) aliases(5) database.
</p>

%PARAM non_fqdn_reject_code 504

<p>
The numerical Postfix SMTP server reply code when a client request
is rejected by the reject_non_fqdn_helo_hostname, reject_non_fqdn_sender
or reject_non_fqdn_recipient restriction.
</p>

%PARAM owner_request_special yes

<p>
Give special treatment to owner-listname and listname-request
address localparts: don't split such addresses when the
recipient_delimiter is set to "-".  This feature is useful for
mailing lists.
</p>

%PARAM permit_mx_backup_networks

<p>
Restrict the use of the permit_mx_backup SMTP access feature to
only domains whose primary MX hosts match the listed networks.
The parameter value syntax is the same as with the mynetworks
parameter; note, however, that the default value is empty.  </p>

%PARAM pickup_service_name pickup

<p>
The name of the pickup(8) service. This service picks up local mail
submissions from the Postfix maildrop queue.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM prepend_delivered_header command, file, forward

<p> The message delivery contexts where the Postfix local(8) delivery
agent prepends a Delivered-To:  message header with the address
that the mail was delivered to. This information is used for mail
delivery loop detection.  </p>

<p>
By default, the Postfix local delivery agent prepends a Delivered-To:
header when forwarding mail and when delivering to file (mailbox)
and command. Turning off the Delivered-To: header when forwarding
mail is not recommended.
</p>

<p>
Specify zero or more of <b>forward</b>, <b>file</b>, or <b>command</b>.
</p>

<p>
Example:
</p>

<pre>
prepend_delivered_header = forward
</pre>

%PARAM process_name read-only

<p>
The process name of a Postfix command or daemon process.
</p>

%PARAM process_id read-only

<p>
The process ID of a Postfix command or daemon process.
</p>

%PARAM process_id_directory pid

<p>
The location of Postfix PID files relative to $queue_directory.
This is a read-only parameter.
</p>

%PARAM proxy_read_maps see "postconf -d" output

<p>
The lookup tables that the proxymap(8) server is allowed to
access for the read-only service.
Table references that don't begin with proxy: are ignored.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM proxy_write_maps see "postconf -d" output

<p> The lookup tables that the proxymap(8) server is allowed to
access for the read-write service. Postfix-owned local database
files should be stored under the Postfix-owned data_directory.
Table references that don't begin with proxy: are ignored.  </p>

<p>
This feature is available in Postfix 2.5 and later.
</p>

%PARAM qmgr_clog_warn_time 300s

<p>
The minimal delay between warnings that a specific destination is
clogging up the Postfix active queue. Specify 0 to disable.
</p>

<p>
This feature is enabled with the helpful_warnings parameter.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM qmgr_fudge_factor 100

<p>
Obsolete feature: the percentage of delivery resources that a busy
mail system will use up for delivery of a large mailing  list
message.
</p>

<p>
This feature exists only in the oqmgr(8) old queue manager. The
current queue manager solves the problem in a better way.
</p>

%PARAM queue_directory see "postconf -d" output

<p>
The location of the Postfix top-level queue directory. This is the
root directory of Postfix daemon processes that run chrooted.
</p>

%PARAM queue_file_attribute_count_limit 100

<p>
The maximal number of (name=value) attributes that may be stored
in a Postfix queue file. The limit is enforced by the cleanup(8)
server.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM queue_service_name qmgr

<p>
The name of the qmgr(8) service. This service manages the Postfix
queue and schedules delivery requests.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM html_directory see "postconf -d" output

<p>
The location of Postfix HTML files that describe how to build,
configure or operate a specific Postfix subsystem or feature.
</p>

%PARAM readme_directory see "postconf -d" output

<p>
The location of Postfix README files that describe how to build,
configure or operate a specific Postfix subsystem or feature.
</p>

%PARAM relay_transport relay

<p>
The default mail delivery transport and next-hop destination for
remote delivery to domains listed with $relay_domains. In order of
decreasing precedence, the nexthop destination is taken from
$relay_transport, $sender_dependent_relayhost_maps, $relayhost, or
from the recipient domain. This information can be overruled with
the transport(5) table.
</p>

<p>
Specify a string of the form <i>transport:nexthop</i>, where <i>transport</i>
is the name of a mail delivery transport defined in master.cf.
The <i>:nexthop</i> destination is optional; its syntax is documented
in the manual page of the corresponding delivery agent.
</p>

<p>
See also the relay domains address class in the ADDRESS_CLASS_README
file.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM rewrite_service_name rewrite

<p>
The name of the address rewriting service. This service rewrites
addresses to standard form and resolves them to a (delivery method,
next-hop host, recipient) triple.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM sample_directory /etc/postfix

<p>
The name of the directory with example Postfix configuration files.
Starting with Postfix 2.1, these files have been replaced with the
postconf(5) manual page.
</p>

%PARAM sender_based_routing no

<p>
This parameter should not be used. It was replaced by sender_dependent_relayhost_maps
in Postfix version 2.3.
</p>

%PARAM sendmail_path see "postconf -d" output

<p>
A Sendmail compatibility feature that specifies the location of
the Postfix sendmail(1) command. This command can be used to
submit mail into the Postfix queue.
</p>

%PARAM service_throttle_time 60s

<p>
How long the Postfix master(8) waits before forking a server that
appears to be malfunctioning.
</p>

<p>
Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).
</p>

%PARAM setgid_group postdrop

<p>
The group ownership of set-gid Postfix commands and of group-writable
Postfix directories. When this parameter value is changed you need
to re-run "<b>postfix set-permissions</b>" (with Postfix version 2.0 and
earlier: "<b>/etc/postfix/post-install set-permissions</b>".
</p>

%PARAM show_user_unknown_table_name yes

<p>
Display the name of the recipient table in the "User unknown"
responses.  The extra detail makes trouble shooting easier but also
reveals information that is nobody elses business.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM showq_service_name showq

<p>
The name of the showq(8) service. This service produces mail queue
status reports.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM smtp_pix_workaround_delay_time 10s

<p>
How long the Postfix SMTP client pauses before sending
".&lt;CR&gt;&lt;LF&gt;" in order to work around the PIX firewall
"&lt;CR&gt;&lt;LF&gt;.&lt;CR&gt;&lt;LF&gt;" bug.
</p>

<p>
Choosing a too short time makes this workaround ineffective when
sending large messages over slow network connections.
</p>

%PARAM smtp_randomize_addresses yes

<p>
Randomize the order of equal-preference MX host addresses.  This
is a performance feature of the Postfix SMTP client.
</p>

%PARAM smtp_rset_timeout 20s

<p> The SMTP client time limit for sending the RSET command, and
for receiving the server response. The SMTP client sends RSET in
order to finish a recipient address probe, or to verify that a
cached session is still usable.  </p>

<p> This feature is available in Postfix 2.1 and later.  </p>

%PARAM smtpd_data_restrictions

<p>
Optional access restrictions that the Postfix SMTP server applies
in the context of the SMTP DATA command.
See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
restriction lists" for a discussion of evaluation context and time.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

<p>
Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first
restriction that matches wins.
</p>

<p>
The following restrictions are valid in this context:
</p>

<ul>

<li><a href="#generic">Generic</a> restrictions that can be used
in any SMTP command context, described under smtpd_client_restrictions.

<li>SMTP command specific restrictions described under
smtpd_client_restrictions, smtpd_helo_restrictions,
smtpd_sender_restrictions or smtpd_recipient_restrictions.

</ul>

<p>
Examples:
</p>

<pre>
smtpd_data_restrictions = reject_unauth_pipelining
smtpd_data_restrictions = reject_multi_recipient_bounce
</pre>

%PARAM smtpd_end_of_data_restrictions

<p> Optional access restrictions that the Postfix SMTP server
applies in the context of the SMTP END-OF-DATA command.
See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
restriction lists" for a discussion of evaluation context and time.
</p>

<p> This feature is available in Postfix 2.2 and later. </p>

<p> See smtpd_data_restrictions for syntax details. </p>

%PARAM smtpd_delay_reject yes

<p>
Wait until the RCPT TO command before evaluating
$smtpd_client_restrictions, $smtpd_helo_restrictions and
$smtpd_sender_restrictions, or wait until the ETRN command before
evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.
</p>

<p>
This feature is turned on by default because some clients apparently
mis-behave when the Postfix SMTP server rejects commands before
RCPT TO.
</p>

<p>
The default setting has one major benefit: it allows Postfix to log
recipient address information when rejecting a client name/address
or sender address, so that it is possible to find out whose mail
is being rejected.
</p>

%PARAM smtpd_null_access_lookup_key &lt;&gt;

<p>
The lookup key to be used in SMTP access(5) tables instead of the
null sender address.
</p>

%CLASS smtpd-policy SMTP server policy delegation

<p>
The Postfix SMTP server has a number of built-in mechanisms to
block or accept mail at specific SMTP protocol stages. As of version
2.1 Postfix can be configured to delegate policy decisions to an
external server that runs outside Postfix. See the file
SMTPD_POLICY_README for more information.
</p>

%PARAM smtpd_policy_service_max_idle 300s

<p>
The time after which an idle SMTPD policy service connection is
closed.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtpd_policy_service_max_ttl 1000s

<p>
The time after which an active SMTPD policy service connection is
closed.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtpd_policy_service_timeout 100s

<p>
The time limit for connecting to, writing to or receiving from a
delegated SMTPD policy server.
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtpd_reject_unlisted_recipient yes

<p>
Request that the Postfix SMTP server rejects mail for unknown
recipient addresses, even when no explicit reject_unlisted_recipient
access restriction is specified. This prevents the Postfix queue
from filling up with undeliverable MAILER-DAEMON messages.
</p>

<p> An address is always considered "known" when it matches a
virtual(5) alias or a canonical(5) mapping.

<ul>

<li> The recipient domain matches $mydestination, $inet_interfaces
or $proxy_interfaces, but the recipient is not listed in
$local_recipient_maps, and $local_recipient_maps is not null.

<li> The recipient domain matches $virtual_alias_domains but the
recipient is not listed in $virtual_alias_maps.

<li> The recipient domain matches $virtual_mailbox_domains but the
recipient is not listed in $virtual_mailbox_maps, and $virtual_mailbox_maps
is not null.

<li> The recipient domain matches $relay_domains but the recipient
is not listed in $relay_recipient_maps, and $relay_recipient_maps
is not null.

</ul>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtpd_reject_unlisted_sender no

<p> Request that the Postfix SMTP server rejects mail from unknown
sender addresses, even when no explicit reject_unlisted_sender
access restriction is specified. This can slow down an explosion
of forged mail from worms or viruses.  </p>

<p> An address is always considered "known" when it matches a
virtual(5) alias or a canonical(5) mapping.

<ul>

<li> The sender domain matches $mydestination, $inet_interfaces or
$proxy_interfaces, but the sender is not listed in
$local_recipient_maps, and $local_recipient_maps is not null.

<li> The sender domain matches $virtual_alias_domains but the sender
is not listed in $virtual_alias_maps.

<li> The sender domain matches $virtual_mailbox_domains but the
sender is not listed in $virtual_mailbox_maps, and $virtual_mailbox_maps
is not null.

<li> The sender domain matches $relay_domains but the sender is
not listed in $relay_recipient_maps, and $relay_recipient_maps is
not null.

</ul>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM smtpd_restriction_classes

<p>
User-defined aliases for groups of access restrictions. The aliases
can be specified in smtpd_recipient_restrictions etc., and on the
right-hand side of a Postfix access(5) table.
</p>

<p>
One major application is for implementing per-recipient UCE control.
See the RESTRICTION_CLASS_README document for other examples.
</p>

%PARAM smtpd_sasl_application_name smtpd

<p>
The application name that the Postfix SMTP server uses for SASL
server initialization. This
controls the name of the SASL configuration file. The default value
is <b>smtpd</b>, corresponding to a SASL configuration file named
<b>smtpd.conf</b>.
</p>

<p>
This feature is available in Postfix 2.1 and 2.2. With Postfix 2.3
it was renamed to smtpd_sasl_path.
</p>

%PARAM strict_7bit_headers no

<p>
Reject mail with 8-bit text in message headers. This blocks mail
from poorly written applications.
</p>

<p>
This feature should not be enabled on a general purpose mail server,
because it is likely to reject legitimate email.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM strict_8bitmime no

<p>
Enable both strict_7bit_headers and strict_8bitmime_body.
</p>

<p>
This feature should not be enabled on a general purpose mail server,
because it is likely to reject legitimate email.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM strict_8bitmime_body no

<p>
Reject 8-bit message body text without 8-bit MIME content encoding
information.  This blocks mail from poorly written applications.
</p>

<p>
Unfortunately, this also rejects majordomo approval requests when
the included request contains valid 8-bit MIME mail, and it rejects
bounces from mailers that do not MIME encapsulate 8-bit content
(for example, bounces from qmail or from old versions of Postfix).
</p>

<p>
This feature should not be enabled on a general purpose mail server,
because it is likely to reject legitimate email.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM strict_mime_encoding_domain no

<p>
Reject mail with invalid Content-Transfer-Encoding: information
for the message/* or multipart/* MIME content types.  This blocks
mail from poorly written software.
</p>

<p>
This feature should not be enabled on a general purpose mail server,
because it will reject mail after a single violation.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM sun_mailtool_compatibility no

<p>
Obsolete SUN mailtool compatibility feature. Instead, use
"mailbox_delivery_lock = dotlock".
</p>

%PARAM trace_service_name trace

<p>
The name of the trace service. This service is implemented by the
bounce(8) daemon and maintains a record
of mail deliveries and produces a mail delivery report when verbose
delivery is requested with "<b>sendmail -v</b>".
</p>

<p>
This feature is available in Postfix 2.1 and later.
</p>

%PARAM undisclosed_recipients_header To: undisclosed-recipients:;

<p>
Message header that the Postfix cleanup(8) server inserts when a
message contains no To: or Cc: message header. With Postfix 2.4
and later, specify an empty value to disable this feature.  </p>

%PARAM unknown_relay_recipient_reject_code 550

<p>
The numerical Postfix SMTP server reply code when a recipient
address matches $relay_domains, and relay_recipient_maps specifies
a list of lookup tables that does not match the recipient address.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM unknown_virtual_alias_reject_code 550

<p>
The SMTP server reply code when a recipient address matches
$virtual_alias_domains, and $virtual_alias_maps specifies a list
of lookup tables that does not match the recipient address.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM unknown_virtual_mailbox_reject_code 550

<p>
The SMTP server reply code when a recipient address matches
$virtual_mailbox_domains, and $virtual_mailbox_maps specifies a list
of lookup tables that does not match the recipient address.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM verp_delimiter_filter -=+

<p>
The characters Postfix accepts as VERP delimiter characters on the
Postfix sendmail(1) command line and in SMTP commands.
</p>

<p>
This feature is available in Postfix 1.1 and later.
</p>

%PARAM virtual_gid_maps

<p>
Lookup tables with the per-recipient group ID for virtual(8) mailbox
delivery.
</p>

<p>
In a lookup table, specify a left-hand side of "@domain.tld" to
match any user in the specified domain that does not have a specific
"user@domain.tld" entry.
</p>

<p>
When a recipient address has an optional address extension
(user+foo@domain.tld), the virtual(8) delivery agent looks up
the full address first, and when the lookup fails, it looks up the
unextended address (user@domain.tld).
</p>

<p>
Note 1: for security reasons, the virtual(8) delivery agent disallows
regular expression substitution of $1 etc. in regular expression
lookup tables, because that would open a security hole.
</p>

<p>
Note 2: for security reasons, the virtual(8) delivery agent will
silently ignore requests to use the proxymap(8) server. Instead
it will open the table directly. Before Postfix version 2.2, the
virtual(8) delivery agent will terminate with a fatal error.
</p>

%PARAM virtual_mailbox_base

<p>
A prefix that the virtual(8) delivery agent prepends to all pathname
results from $virtual_mailbox_maps table lookups.  This is a safety
measure to ensure that an out of control map doesn't litter the
file system with mailboxes.  While virtual_mailbox_base could be
set to "/", this setting isn't recommended.
</p>

<p>
Example:
</p>

<pre>
virtual_mailbox_base = /var/mail
</pre>

%PARAM virtual_mailbox_domains $virtual_mailbox_maps

<p> Postfix is final destination for the specified list of domains;
mail is delivered via the $virtual_transport mail delivery transport.
By default this is the Postfix virtual(8) delivery agent.  The SMTP
server validates recipient addresses with $virtual_mailbox_maps
and rejects mail for non-existent recipients.  See also the virtual
mailbox domain class in the ADDRESS_CLASS_README file.  </p>

<p> This parameter expects the same syntax as the mydestination
configuration parameter.  </p>

<p>
This feature is available in Postfix 2.0 and later. The default
value is backwards compatible with Postfix version 1.1.
</p>

%PARAM virtual_mailbox_limit 51200000

<p>
The maximal size in bytes of an individual virtual(8) mailbox or
maildir file, or zero (no limit).  </p>

%PARAM virtual_mailbox_lock see "postconf -d" output

<p>
How to lock a UNIX-style virtual(8) mailbox before attempting
delivery.  For a list of available file locking methods, use the
"<b>postconf -l</b>" command.
</p>

<p>
This setting is ignored with <b>maildir</b> style delivery, because
such deliveries are safe without application-level locks.
</p>

<p>
Note 1: the <b>dotlock</b> method requires that the recipient UID
or GID has write access to the parent directory of the recipient's
mailbox file.
</p>

<p>
Note 2: the default setting of this parameter is system dependent.
</p>

%PARAM virtual_mailbox_maps

<p>
Optional lookup tables with all valid addresses in the domains that
match $virtual_mailbox_domains.
</p>

<p>
In a lookup table, specify a left-hand side of "@domain.tld" to
match any user in the specified domain that does not have a specific
"user@domain.tld" entry.
</p>

<p>
The virtual(8) delivery agent uses this table to look up the
per-recipient mailbox or maildir pathname.  If the lookup result
ends in a slash ("/"), maildir-style delivery is carried out,
otherwise the path is assumed to specify a UNIX-style mailbox file.
Note that $virtual_mailbox_base is unconditionally prepended to
this path.
</p>

<p>
When a recipient address has an optional address extension
(user+foo@domain.tld), the virtual(8) delivery agent looks up
the full address first, and when the lookup fails, it looks up the
unextended address (user@domain.tld).
</p>

<p>
Note 1: for security reasons, the virtual(8) delivery agent disallows
regular expression substitution of $1 etc. in regular expression
lookup tables, because that would open a security hole.
</p>

<p>
Note 2: for security reasons, the virtual(8) delivery agent will
silently ignore requests to use the proxymap(8) server. Instead
it will open the table directly. Before Postfix version 2.2, the
virtual(8) delivery agent will terminate with a fatal error.
</p>

%PARAM virtual_minimum_uid 100

<p>
The minimum user ID value that the virtual(8) delivery agent accepts
as a result from $virtual_uid_maps table lookup.  Returned
values less than this will be rejected, and the message will be
deferred.
</p>

%PARAM virtual_transport virtual

<p>
The default mail delivery transport and next-hop destination for
final delivery to domains listed with $virtual_mailbox_domains.
This information can be overruled with the transport(5) table.
</p>

<p>
Specify a string of the form <i>transport:nexthop</i>, where <i>transport</i>
is the name of a mail delivery transport defined in master.cf.
The <i>:nexthop</i> destination is optional; its syntax is documented
in the manual page of the corresponding delivery agent.
</p>

<p>
This feature is available in Postfix 2.0 and later.
</p>

%PARAM virtual_uid_maps

<p>
Lookup tables with the per-recipient user ID that the virtual(8)
delivery agent uses while writing to the recipient's mailbox.
</p>

<p>
In a lookup table, specify a left-hand side of "@domain.tld"
to match any user in the specified domain that does not have a
specific "user@domain.tld" entry.
</p>

<p>
When a recipient address has an optional address extension
(user+foo@domain.tld), the virtual(8) delivery agent looks up
the full address first, and when the lookup fails, it looks up the
unextended address (user@domain.tld).
</p>

<p>
Note 1: for security reasons, the virtual(8) delivery agent disallows
regular expression substitution of $1 etc. in regular expression
lookup tables, because that would open a security hole.
</p>

<p>
Note 2: for security reasons, the virtual(8) delivery agent will
silently ignore requests to use the proxymap(8) server. Instead
it will open the table directly. Before Postfix version 2.2, the
virtual(8) delivery agent will terminate with a fatal error.
</p>

%PARAM config_directory see "postconf -d" output

<p> The default location of the Postfix main.cf and master.cf
configuration files. This can be overruled via the following
mechanisms: </p>

<ul>

<li> <p> The MAIL_CONFIG environment variable (daemon processes
and commands). </p>

<li> <p> The "-c" command-line option (commands only). </p>

</ul>

<p> With Postfix command that run with set-gid privileges, a
config_directory override requires either root privileges, or it
requires that the directory is listed with the alternate_config_directories
parameter in the default main.cf file.  </p>

%PARAM virtual_maps

<p> Optional lookup tables with a) names of domains for which all
addresses are aliased to addresses in other local or remote domains,
and b) addresses that are aliased to addresses in other local or
remote domains.  Available before Postfix version 2.0. With Postfix
version 2.0 and later, this is replaced by separate controls: virtual_alias_domains
and virtual_alias_maps. </p>

%PARAM smtp_discard_ehlo_keywords

<p> A case insensitive list of EHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix SMTP client will ignore in the EHLO
response from a remote SMTP server. </p>

<p> This feature is available in Postfix 2.2 and later. </p>

<p> Notes: </p>

<ul>

<li> <p> Specify the <b>silent-discard</b> pseudo keyword to prevent
this action from being logged. </p>

<li> <p> Use the smtp_discard_ehlo_keyword_address_maps feature to
discard EHLO keywords selectively. </p>

</ul>

%PARAM smtpd_discard_ehlo_keywords

<p> A case insensitive list of EHLO keywords (pipelining, starttls,
auth, etc.) that the SMTP server will not send in the EHLO response
to a remote SMTP client. </p>

<p> This feature is available in Postfix 2.2 and later. </p>

<p> Notes: </p>

<ul>

<li> <p> Specify the <b>silent-discard</b> pseudo keyword to prevent
this action from being logged. </p>

<li> <p> Use the smtpd_discard_ehlo_keyword_address_maps feature
to discard EHLO keywords selectively.  </p>

</ul>

%PARAM smtp_discard_ehlo_keyword_address_maps

<p> Lookup tables, indexed by the remote SMTP server address, with
case insensitive lists of EHLO keywords (pipelining, starttls, auth,
etc.) that the Postfix SMTP client will ignore in the EHLO response from a
remote SMTP server. See smtp_discard_ehlo_keywords for details. The
table is not indexed by hostname for consistency with
smtpd_discard_ehlo_keyword_address_maps. </p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM smtpd_discard_ehlo_keyword_address_maps

<p> Lookup tables, indexed by the remote SMTP client address, with
case insensitive lists of EHLO keywords (pipelining, starttls, auth,
etc.) that the SMTP server will not send in the EHLO response to a
remote SMTP client. See smtpd_discard_ehlo_keywords for details.
The table is not searched by hostname for robustness reasons.  </p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM connection_cache_service_name scache

<p> The name of the scache(8) connection cache service.  This service
maintains a limited pool of cached sessions.  </p>

<p> This feature is available in Postfix 2.2 and later. </p>

%PARAM connection_cache_ttl_limit 2s

<p> The maximal time-to-live value that the scache(8) connection
cache server
allows. Requests that specify a larger TTL will be stored with the
maximum allowed TTL. The purpose of this additional control is to
protect the infrastructure against careless people. The cache TTL
is already bounded by $max_idle.  </p>

%PARAM connection_cache_status_update_time 600s

<p> How frequently the scache(8) server logs usage statistics with
connection cache hit and miss rates for logical destinations and for
physical endpoints. </p>

%PARAM remote_header_rewrite_domain

<p> Don't rewrite message headers from remote clients at all when
this parameter is empty; otherwise, rewrite message headers and
append the specified domain name to incomplete addresses.  The
local_header_rewrite_clients parameter controls what clients Postfix
considers local. </p>

<p> Examples:  </p>

<p> The safe setting: append "domain.invalid" to incomplete header
addresses from remote SMTP clients, so that those addresses cannot
be confused with local addresses. </p>

<blockquote>
<pre>
remote_header_rewrite_domain = domain.invalid
</pre>
</blockquote>

<p> The default, purist, setting: don't rewrite headers from remote
clients at all. </p>

<blockquote>
<pre>
remote_header_rewrite_domain =
</pre>
</blockquote>

%PARAM local_header_rewrite_clients permit_inet_interfaces

<p> Rewrite message header addresses in mail from these clients and
update incomplete addresses with the domain name in $myorigin or
$mydomain; either don't rewrite message headers from other clients
at all, or rewrite message headers and update incomplete addresses
with the domain specified in the remote_header_rewrite_domain
parameter.  </p>

<p> See the append_at_myorigin and append_dot_mydomain parameters
for details of how domain names are appended to incomplete addresses.
</p>

<p> Specify a list of zero or more of the following:  </p>

<dl>

<dt><b>permit_inet_interfaces</b></dt>

<dd> Append the domain name in $myorigin or $mydomain when the
client IP address matches $inet_interfaces. This is enabled by
default. </dd>

<dt><b>permit_mynetworks</b></dt>

<dd> Append the domain name in $myorigin or $mydomain when the
client IP address matches any network or network address listed in
$mynetworks. This setting will not prevent remote mail header
address rewriting when mail from a remote client is forwarded by
a neighboring system.  </dd>

<dt><b>permit_sasl_authenticated </b></dt>

<dd> Append the domain name in $myorigin or $mydomain when the
client is successfully authenticated via the RFC 4954 (AUTH)
protocol. </dd>

<dt><b>permit_tls_clientcerts </b></dt>

<dd> Append the domain name in $myorigin or $mydomain when the
client TLS certificate fingerprint is listed in $relay_clientcerts.
The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to
Postfix version 2.5).  </dd>

<dt><b>permit_tls_all_clientcerts </b></dt>

<dd> Append the domain name in $myorigin or $mydomain when the
client TLS certificate is successfully verified, regardless of
whether it is listed on the server, and regardless of the certifying
authority. </dd>

<dt><b><a name="check_address_map">check_address_map</a> <i><a href="DATABASE_README.html">type:table</a></i> </b></dt>

<dt><b><i><a href="DATABASE_README.html">type:table</a></i> </b></dt>

<dd> Append the domain name in $myorigin or $mydomain when the
client IP address matches the specified lookup table.
The lookup result is ignored, and no subnet lookup is done. This
is suitable for, e.g., pop-before-smtp lookup tables. </dd>

</dl>

<p> Examples:  </p>

<p> The Postfix &lt; 2.2 backwards compatible setting: always rewrite
message headers, and always append my own domain to incomplete
header addresses.  </p>

<blockquote>
<pre>
local_header_rewrite_clients = static:all
</pre>
</blockquote>

<p> The purist (and default) setting: rewrite headers only in mail
from Postfix sendmail and in SMTP mail from this machine. </p>

<blockquote>
<pre>
local_header_rewrite_clients = permit_inet_interfaces
</pre>
</blockquote>

<p> The intermediate setting: rewrite header addresses and append
$myorigin or $mydomain information only with mail from Postfix
sendmail, from local clients, or from authorized SMTP clients. </p>

<p> Note: this setting will not prevent remote mail header address
rewriting when mail from a remote client is forwarded by a neighboring
system.  </p>

<blockquote>
<pre>
local_header_rewrite_clients = permit_mynetworks,
    permit_sasl_authenticated permit_tls_clientcerts
    check_address_map hash:/etc/postfix/pop-before-smtp
</pre>
</blockquote>

%PARAM smtpd_tls_cert_file

<p> File with the Postfix SMTP server RSA certificate in PEM format.
This file may also contain the Postfix SMTP server private RSA key. </p>

<p> Public Internet MX hosts without certificates signed by a "reputable"
CA must generate, and be prepared to present to most clients, a
self-signed or private-CA signed certificate. The client will not be
able to authenticate the server, but unless it is running Postfix 2.3 or
similar software, it will still insist on a server certificate. </p>

<p> For servers that are <b>not</b> public Internet MX hosts, Postfix
2.3 supports configurations with no certificates. This entails the
use of just the anonymous TLS ciphers, which are not supported by
typical SMTP clients. Since such clients will not, as a rule, fall
back to plain text after a TLS handshake failure, the server will
be unable to receive email from TLS enabled clients. To avoid
accidental configurations with no certificates, Postfix 2.3 enables
certificate-less operation only when the administrator explicitly
sets "smtpd_tls_cert_file = none". This ensures that new Postfix
configurations will not accidentally run with no certificates. </p>

<p> Both RSA and DSA certificates are supported.  When both types
are present, the cipher used determines which certificate will be
presented to the client.  For Netscape and OpenSSL clients without
special cipher choices the RSA certificate is preferred. </p>

<p> To enable a remote SMTP client to verify the Postfix SMTP server
certificate, the issuing CA certificates must be made available to the
client. You should include the required certificates in the server
certificate file, the server certificate first, then the issuing
CA(s) (bottom-up order). </p>

<p> Example: the certificate for "server.example.com" was issued by
"intermediate CA" which itself has a certificate of "root CA".
Create the server.pem file with "cat server_cert.pem intermediate_CA.pem
root_CA.pem &gt; server.pem". </p>

<p> If you also want to verify client certificates issued by these
CAs, you can add the CA certificates to the smtpd_tls_CAfile, in which
case it is not necessary to have them in the smtpd_tls_cert_file or
smtpd_tls_dcert_file. </p>

<p> A certificate supplied here must be usable as an SSL server certificate
and hence pass the "openssl verify -purpose sslserver ..." test. </p>

<p> Example: </p>

<pre>
smtpd_tls_cert_file = /etc/postfix/server.pem
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_key_file $smtpd_tls_cert_file

<p> File with the Postfix SMTP server RSA private key in PEM format.
This file may be combined with the Postfix SMTP server RSA certificate
file specified with $smtpd_tls_cert_file. </p>

<p> The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account ("root"), and no access
to anyone else. </p>

%PARAM smtpd_tls_dcert_file

<p> File with the Postfix SMTP server DSA certificate in PEM format.
This file may also contain the Postfix SMTP server private DSA key. </p>

<p> See the discussion under smtpd_tls_cert_file for more details.
</p>

<p> Example: </p>

<pre>
smtpd_tls_dcert_file = /etc/postfix/server-dsa.pem
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_dkey_file $smtpd_tls_dcert_file

<p> File with the Postfix SMTP server DSA private key in PEM format.
This file may be combined with the Postfix SMTP server DSA certificate
file specified with $smtpd_tls_dcert_file. </p>

<p> The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account ("root"), and no access
to anyone else. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_CAfile

<p> A file containing (PEM format) CA certificates of root CAs trusted
to sign either remote SMTP client certificates or intermediate CA
certificates.  These are loaded into memory before the smtpd(8) server
enters the chroot jail. If the number of trusted roots is large, consider
using smtpd_tls_CApath instead, but note that the latter directory must
be present in the chroot jail if the smtpd(8) server is chrooted. This
file may also be used to augment the server certificate trust chain,
but it is best to include all the required certificates directly in the
server certificate file. </p>

<p> Specify "tls_append_default_CA = no" to prevent Postfix from
appending the system-supplied default CAs and trusting third-party
certificates. </p>

<p> By default (see smtpd_tls_ask_ccert), client certificates are not
requested, and smtpd_tls_CAfile should remain empty. If you do make use
of client certificates, the distinguished names (DNs) of the certificate
authorities listed in smtpd_tls_CAfile are sent to the remote SMTP client
in the client certificate request message. MUAs with multiple client
certificates may use the list of preferred certificate authorities
to select the correct client certificate.  You may want to put your
"preferred" CA or CAs in this file, and install other trusted CAs in
$smtpd_tls_CApath. </p>

<p> Example: </p>

<pre>
smtpd_tls_CAfile = /etc/postfix/CAcert.pem
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_CApath

<p> A directory containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or intermediate CA
certificates. Do not forget to create the necessary "hash" links with,
for example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs". To use
smtpd_tls_CApath in chroot mode, this directory (or a copy) must be
inside the chroot jail. </p>

<p> Specify "tls_append_default_CA = no" to prevent Postfix from
appending the system-supplied default CAs and trusting third-party
certificates. </p>

<p> By default (see smtpd_tls_ask_ccert), client certificates are
not requested, and smtpd_tls_CApath should remain empty. In contrast
to smtpd_tls_CAfile, DNs of certificate authorities installed
in $smtpd_tls_CApath are not included in the client certificate
request message. MUAs with multiple client certificates may use the
list of preferred certificate authorities to select the correct
client certificate.  You may want to put your "preferred" CA or
CAs in $smtpd_tls_CAfile, and install the remaining trusted CAs in
$smtpd_tls_CApath. </p>

<p> Example: </p>

<pre>
smtpd_tls_CApath = /etc/postfix/certs
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_loglevel 0

<p> Enable additional Postfix SMTP server logging of TLS activity.
Each logging level also includes the information that is logged at
a lower logging level.  </p>

<dl compact>

<dt> </dt> <dd> 0 Disable logging of TLS activity. </dd>

<dt> </dt> <dd> 1 Log TLS handshake and certificate information. </dd>

<dt> </dt> <dd> 2 Log levels during TLS negotiation. </dd>

<dt> </dt> <dd> 3 Log hexadecimal and ASCII dump of TLS negotiation
process.  </dd>

<dt> </dt> <dd> 4 Also log hexadecimal and ASCII dump of complete
transmission after STARTTLS. </dd>

</dl>

<p> Use "smtpd_tls_loglevel = 3" only in case of problems. Use of
loglevel 4 is strongly discouraged. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_received_header no

<p> Request that the Postfix SMTP server produces Received:  message
headers that include information about the protocol and cipher used,
as well as the client CommonName and client certificate issuer
CommonName.  This is disabled by default, as the information may
be modified in transit through other mail servers.  Only information
that was recorded by the final destination can be trusted. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_use_tls no

<p> Opportunistic TLS: announce STARTTLS support to SMTP clients,
but do not require that clients use TLS encryption. </p>

<p> Note: when invoked via "<b>sendmail -bs</b>", Postfix will never offer
STARTTLS due to insufficient privileges to access the server private
key. This is intended behavior. </p>

<p> This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtpd_tls_security_level instead. </p>

%PARAM smtpd_enforce_tls no

<p> Mandatory TLS: announce STARTTLS support to SMTP clients,
and require that clients use TLS encryption.  According to RFC 2487
this MUST NOT be applied in case of a publicly-referenced SMTP
server.  This option is off by default and should be used only on
dedicated servers. </p>

<p> Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes". </p>

<p> Note 2: when invoked via "<b>sendmail -bs</b>", Postfix will never offer
STARTTLS due to insufficient privileges to access the server private
key. This is intended behavior. </p>

<p> This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtpd_tls_security_level instead. </p>

%PARAM smtpd_tls_wrappermode no

<p> Run the Postfix SMTP server in the non-standard "wrapper" mode,
instead of using the STARTTLS command. </p>

<p> If you want to support this service, enable a special port in
master.cf, and specify "-o smtpd_tls_wrappermode=yes" on the SMTP
server's command line. Port 465 (smtps) was once chosen for this
purpose. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_ask_ccert no

<p> Ask a remote SMTP client for a client certificate. This
information is needed for certificate based mail relaying with,
for example, the permit_tls_clientcerts feature. </p>

<p> Some clients such as Netscape will either complain if no
certificate is available (for the list of CAs in $smtpd_tls_CAfile)
or will offer multiple client certificates to choose from. This
may be annoying, so this option is "off" by default. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_req_ccert no

<p> With mandatory TLS encryption, require a trusted remote SMTP client
certificate in order to allow TLS connections to proceed.  This
option implies "smtpd_tls_ask_ccert = yes". </p>

<p> When TLS encryption is optional, this setting is ignored with
a warning written to the mail log. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_ccert_verifydepth 9

<p> The verification depth for remote SMTP client certificates. A
depth of 1 is sufficient if the issuing CA is listed in a local CA
file. </p>

<p> The default verification depth is 9 (the OpenSSL default) for
compatibility with earlier Postfix behavior. Prior to Postfix 2.5,
the default value was 5, but the limit was not actually enforced. If
you have set this to a lower non-default value, certificates with longer
trust chains may now fail to verify. Certificate chains with 1 or 2
CAs are common, deeper chains are more rare and any number between 5
and 9 should suffice in practice. You can choose a lower number if,
for example, you trust certificates directly signed by an issuing CA
but not any CAs it delegates to. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_auth_only no

<p> When TLS encryption is optional in the Postfix SMTP server, do
not announce or accept SASL authentication over unencrypted
connections. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_session_cache_database

<p> Name of the file containing the optional Postfix SMTP server
TLS session cache. Specify a database type that supports enumeration,
such as <b>btree</b> or <b>sdbm</b>; there is no need to support
concurrent access.  The file is created if it does not exist. The smtpd(8)
daemon does not use this parameter directly, rather the cache is
implemented indirectly in the tlsmgr(8) daemon. This means that
per-smtpd-instance master.cf overrides of this parameter are not
effective. Note, that each of the cache databases supported by tlsmgr(8)
daemon: $smtpd_tls_session_cache_database, $smtp_tls_session_cache_database
(and with Postfix 2.3 and later $lmtp_tls_session_cache_database), needs to be
stored separately. It is not at this time possible to store multiple
caches in a single database. </p>

<p> Note: <b>dbm</b> databases are not suitable. TLS
session objects are too large. </p>

<p> As of version 2.5, Postfix no longer uses root privileges when
opening this file. The file should now be stored under the Postfix-owned
data_directory. As a migration aid, an attempt to open the file
under a non-Postfix directory is redirected to the Postfix-owned
data_directory, and a warning is logged. </p>

<p> Example: </p>

<pre>
smtpd_tls_session_cache_database = btree:/var/db/postfix/smtpd_scache
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_tls_session_cache_timeout 3600s

<p> The expiration time of Postfix SMTP server TLS session cache
information. A cache cleanup is performed periodically
every $smtpd_tls_session_cache_timeout seconds. As with
$smtpd_tls_session_cache_database, this parameter is implemented in the
tlsmgr(8) daemon and therefore per-smtpd-instance master.cf overrides
are not possible. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM relay_clientcerts

<p> List of tables with remote SMTP client-certificate fingerprints
for which the Postfix SMTP server will allow access with the
permit_tls_clientcerts feature.
The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior to
Postfix version 2.5).  </p>

<p> Postfix lookup tables are in the form of (key, value) pairs.
Since we only need the key, the value can be chosen freely, e.g.
the name of the user or host:
D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80 lutzpc.at.home </p>

<p> Example: </p>

<pre>
relay_clientcerts = hash:/etc/postfix/relay_clientcerts
</pre>

<p>For more fine-grained control, use check_ccert_access to select
an appropriate access(5) policy for each client.
See RESTRICTION_CLASS_README.</p>

<p>This feature is available with Postfix version 2.2.</p>

%PARAM smtpd_tls_cipherlist

<p> Obsolete Postfix &lt; 2.3 control for the Postfix SMTP server TLS
cipher list. It is easy to create inter-operability problems by choosing
a non-default cipher list. Do not use a non-default TLS cipherlist for
MX hosts on the public Internet. Clients that begin the TLS handshake,
but are unable to agree on a common cipher, may not be able to send any
email to the SMTP server. Using a restricted cipher list may be more
appropriate for a dedicated MSA or an internal mailhub, where one can
exert some control over the TLS software and settings of the connecting
clients. </p>

<p> <b>Note:</b> do not use "" quotes around the parameter value. </p>

<p>This feature is available with Postfix version 2.2. It is not used with
Postfix 2.3 and later; use smtpd_tls_mandatory_ciphers instead. </p>

%PARAM smtpd_tls_dh1024_param_file

<p> File with DH parameters that the Postfix SMTP server should
use with EDH ciphers. </p>

<p> Instead of using the exact same parameter sets as distributed
with other TLS packages, it is more secure to generate your own
set of parameters with something like the following command:  </p>

<blockquote>
<pre>
openssl gendh -out /etc/postfix/dh_1024.pem -2 1024
</pre>
</blockquote>

<p> Your actual source for entropy may differ. Some systems have
/dev/random; on other system you may consider using the "Entropy
Gathering Daemon EGD", available at http://egd.sourceforge.net/
</p>

<p> Example: </p>

<pre>
smtpd_tls_dh1024_param_file = /etc/postfix/dh_1024.pem
</pre>

<p>This feature is available with Postfix version 2.2.</p>

%PARAM smtpd_tls_dh512_param_file

<p> File with DH parameters that the Postfix SMTP server should
use with EDH ciphers. </p>

<p> See also the discussion under the smtpd_tls_dh1024_param_file
configuration parameter.  </p>

<p> Example: </p>

<pre>
smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem
</pre>

<p>This feature is available with Postfix version 2.2.</p>

%PARAM smtpd_starttls_timeout 300s

<p> The time limit for Postfix SMTP server write and read operations
during TLS startup and shutdown handshake procedures. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_cert_file

<p> File with the Postfix SMTP client RSA certificate in PEM format.
This file may also contain the Postfix SMTP client private RSA key,
and these may be the same as the Postfix SMTP server RSA certificate and key
file. </p>

<p> Do not configure client certificates unless you <b>must</b> present
client TLS certificates to one or more servers. Client certificates are
not usually needed, and can cause problems in configurations that work
well without them. The recommended setting is to let the defaults stand: </p>

<blockquote>
<pre>
smtp_tls_cert_file =
smtp_tls_key_file =
smtp_tls_dcert_file =
smtp_tls_dkey_file =
smtp_tls_eccert_file =
smtp_tls_eckey_file =
</pre>
</blockquote>

<p> The best way to use the default settings is to comment out the above
parameters in main.cf if present. </p>

<p> To enable remote SMTP servers to verify the Postfix SMTP client
certificate, the issuing CA certificates must be made available to the
server. You should include the required certificates in the client
certificate file, the client certificate first, then the issuing
CA(s) (bottom-up order). </p>

<p> Example: the certificate for "client.example.com" was issued by
"intermediate CA" which itself has a certificate issued by "root CA".
Create the client.pem file with "cat client_cert.pem intermediate_CA.pem
root_CA.pem &gt; client.pem". </p>

<p> If you also want to verify remote SMTP server certificates issued by
these CAs, you can add the CA certificates to the smtp_tls_CAfile, in
which case it is not necessary to have them in the smtp_tls_cert_file,
smtp_tls_dcert_file or smtp_tls_eccert_file. </p>

<p> A certificate supplied here must be usable as an SSL client certificate
and hence pass the "openssl verify -purpose sslclient ..." test. </p>

<p> Example: </p>

<pre>
smtp_tls_cert_file = /etc/postfix/client.pem
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_key_file $smtp_tls_cert_file

<p> File with the Postfix SMTP client RSA private key in PEM format.
This file may be combined with the Postfix SMTP client RSA certificate
file specified with $smtp_tls_cert_file. </p>

<p> The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account ("root"), and no access
to anyone else. </p>

<p> Example: </p>

<pre>
smtp_tls_key_file = $smtp_tls_cert_file
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_CAfile

<p> A file containing CA certificates of root CAs trusted to sign
either remote SMTP server certificates or intermediate CA certificates.
These are loaded into memory before the smtp(8) client enters the
chroot jail. If the number of trusted roots is large, consider using
smtp_tls_CApath instead, but note that the latter directory must be
present in the chroot jail if the smtp(8) client is chrooted. This
file may also be used to augment the client certificate trust chain,
but it is best to include all the required certificates directly in
$smtp_tls_cert_file. </p>

<p> Specify "tls_append_default_CA = no" to prevent Postfix from
appending the system-supplied default CAs and trusting third-party
certificates. </p>

<p> Example: </p>

<pre>
smtp_tls_CAfile = /etc/postfix/CAcert.pem
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_CApath

<p> Directory with PEM format certificate authority certificates
that the Postfix SMTP client uses to verify a remote SMTP server
certificate.  Don't forget to create the necessary "hash" links
with, for example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".
</p>

<p> To use this option in chroot mode, this directory (or a copy)
must be inside the chroot jail. </p>

<p> Specify "tls_append_default_CA = no" to prevent Postfix from
appending the system-supplied default CAs and trusting third-party
certificates. </p>

<p> Example: </p>

<pre>
smtp_tls_CApath = /etc/postfix/certs
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_loglevel 0

<p> Enable additional Postfix SMTP client logging of TLS activity.
Each logging level also includes the information that is logged at
a lower logging level.  </p>

<dl compact>

<dt> </dt> <dd> 0 Disable logging of TLS activity. </dd>

<dt> </dt> <dd> 1 Log TLS handshake and certificate information. </dd>

<dt> </dt> <dd> 2 Log levels during TLS negotiation. </dd>

<dt> </dt> <dd> 3 Log hexadecimal and ASCII dump of TLS negotiation
process.  </dd>

<dt> </dt> <dd> 4 Log hexadecimal and ASCII dump of complete
transmission after STARTTLS. </dd>

</dl>

<p> Use "smtp_tls_loglevel = 3" only in case of problems. Use of
loglevel 4 is strongly discouraged. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_session_cache_database

<p> Name of the file containing the optional Postfix SMTP client
TLS session cache. Specify a database type that supports enumeration,
such as <b>btree</b> or <b>sdbm</b>; there is no need to support
concurrent access.  The file is created if it does not exist. The smtp(8)
daemon does not use this parameter directly, rather the cache is
implemented indirectly in the tlsmgr(8) daemon. This means that
per-smtp-instance master.cf overrides of this parameter are not effective.
Note, that each of the cache databases supported by tlsmgr(8) daemon:
$smtpd_tls_session_cache_database, $smtp_tls_session_cache_database
(and with Postfix 2.3 and later $lmtp_tls_session_cache_database), needs to
be stored separately. It is not at this time possible to store multiple
caches in a single database. </p>

<p> Note: <b>dbm</b> databases are not suitable. TLS
session objects are too large. </p>

<p> As of version 2.5, Postfix no longer uses root privileges when
opening this file. The file should now be stored under the Postfix-owned
data_directory. As a migration aid, an attempt to open the file
under a non-Postfix directory is redirected to the Postfix-owned
data_directory, and a warning is logged. </p>

<p> Example: </p>

<pre>
smtp_tls_session_cache_database = btree:/var/db/postfix/smtp_scache
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_session_cache_timeout 3600s

<p> The expiration time of Postfix SMTP client TLS session cache
information.  A cache cleanup is performed periodically
every $smtp_tls_session_cache_timeout seconds. As with
$smtp_tls_session_cache_database, this parameter is implemented in the
tlsmgr(8) daemon and therefore per-smtp-instance master.cf overrides
are not possible. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_use_tls no

<p> Opportunistic mode: use TLS when a remote SMTP server announces
STARTTLS support, otherwise send the mail in the clear. Beware:
some SMTP servers offer STARTTLS even if it is not configured.  With
Postfix &lt; 2.3, if the TLS handshake fails, and no other server is
available, delivery is deferred and mail stays in the queue. If this
is a concern for you, use the smtp_tls_per_site feature instead.  </p>

<p> This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtp_tls_security_level instead. </p>

%PARAM smtp_enforce_tls no

<p> Enforcement mode: require that remote SMTP servers use TLS
encryption, and never send mail in the clear.  This also requires
that the remote SMTP server hostname matches the information in
the remote server certificate, and that the remote SMTP server
certificate was issued by a CA that is trusted by the Postfix SMTP
client. If the certificate doesn't verify or the hostname doesn't
match, delivery is deferred and mail stays in the queue.  </p>

<p> The server hostname is matched against all names provided as
dNSNames in the SubjectAlternativeName.  If no dNSNames are specified,
the CommonName is checked.  The behavior may be changed with the
smtp_tls_enforce_peername option.  </p>

<p> This option is useful only if you are definitely sure that you
will only connect to servers that support RFC 2487 _and_ that
provide valid server certificates.  Typical use is for clients that
send all their email to a dedicated mailhub.  </p>

<p> This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtp_tls_security_level instead. </p>

%PARAM smtp_tls_enforce_peername yes

<p> With mandatory TLS encryption, require that the remote SMTP
server hostname matches the information in the remote SMTP server
certificate.  As of RFC 2487 the requirements for hostname checking
for MTA clients are not specified. </p>

<p> This option can be set to "no" to disable strict peer name
checking. This setting has no effect on sessions that are controlled
via the smtp_tls_per_site table.  </p>

<p> Disabling the hostname verification can make sense in closed
environment where special CAs are created.  If not used carefully,
this option opens the danger of a "man-in-the-middle" attack (the
CommonName of this attacker will be logged). </p>

<p> This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtp_tls_security_level instead. </p>

%PARAM smtp_tls_per_site

<p> Optional lookup tables with the Postfix SMTP client TLS usage
policy by next-hop destination and by remote SMTP server hostname.
When both lookups succeed, the more specific per-site policy (NONE,
MUST, etc) overrides the less specific one (MAY), and the more secure
per-site policy (MUST, etc) overrides the less secure one (NONE).
With Postfix 2.3 and later smtp_tls_per_site is strongly discouraged:
use smtp_tls_policy_maps instead. </p>

<p> Use of the bare hostname as the per-site table lookup key is
discouraged. Always use the full destination nexthop (enclosed in
[] with a possible ":port" suffix). A recipient domain or MX-enabled
transport next-hop with no port suffix may look like a bare hostname,
but is still a suitable <i>destination</i>. </p>

<p> Specify a next-hop destination or server hostname on the left-hand
side; no wildcards are allowed. The next-hop destination is either
the recipient domain, or the destination specified with a transport(5)
table, the relayhost parameter, or the relay_transport parameter.
On the right hand side specify one of the following keywords:  </p>

<dl>

<dt> NONE </dt> <dd> Don't use TLS at all. This overrides a less
specific <b>MAY</b> lookup result from the alternate host or next-hop
lookup key, and overrides the global smtp_use_tls, smtp_enforce_tls,
and smtp_tls_enforce_peername settings. </dd>

<dt> MAY </dt> <dd> Try to use TLS if the server announces support,
otherwise use the unencrypted connection. This has less precedence
than a more specific result (including <b>NONE</b>) from the alternate
host or next-hop lookup key, and has less precedence than the more
specific global "smtp_enforce_tls = yes" or "smtp_tls_enforce_peername
= yes".  </dd>

<dt> MUST_NOPEERMATCH </dt> <dd> Require TLS encryption, but do not
require that the remote SMTP server hostname matches the information
in the remote SMTP server certificate, or that the server certificate
was issued by a trusted CA. This overrides a less secure <b>NONE</b>
or a less specific <b>MAY</b> lookup result from the alternate host
or next-hop lookup key, and overrides the global smtp_use_tls,
smtp_enforce_tls and smtp_tls_enforce_peername settings.  </dd>

<dt> MUST </dt> <dd> Require TLS encryption, require that the remote
SMTP server hostname matches the information in the remote SMTP
server certificate, and require that the remote SMTP server certificate
was issued by a trusted CA. This overrides a less secure <b>NONE</b>
and <b>MUST_NOPEERMATCH</b> or a less specific <b>MAY</b> lookup
result from the alternate host or next-hop lookup key, and overrides
the global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peername
settings.  </dd>

</dl>

<p> The above keywords correspond to the "none", "may", "encrypt" and
"verify" security levels for the new smtp_tls_security_level parameter
introduced in Postfix 2.3. Starting with Postfix 2.3, and independently
of how the policy is specified, the smtp_tls_mandatory_ciphers and
smtp_tls_mandatory_protocols parameters apply when TLS encryption
is mandatory. Connections for which encryption is optional typically
enable all "export" grade and better ciphers (see smtp_tls_ciphers
and smtp_tls_protocols). </p>

<p> As long as no secure DNS lookup mechanism is available, false
hostnames in MX or CNAME responses can change the server hostname
that Postfix uses for TLS policy lookup and server certificate
verification. Even with a perfect match between the server hostname and
the server certificate, there is no guarantee that Postfix is connected
to the right server.  See TLS_README (Closing a DNS loophole with obsolete
per-site TLS policies) for a possible work-around. </p>

<p> This feature is available in Postfix 2.2 and later. With
Postfix 2.3 and later use smtp_tls_policy_maps instead. </p>

%PARAM smtp_tls_scert_verifydepth 9

<p> The verification depth for remote SMTP server certificates. A depth
of 1 is sufficient if the issuing CA is listed in a local CA file. </p>

<p> The default verification depth is 9 (the OpenSSL default) for
compatibility with earlier Postfix behavior. Prior to Postfix 2.5,
the default value was 5, but the limit was not actually enforced. If
you have set this to a lower non-default value, certificates with longer
trust chains may now fail to verify. Certificate chains with 1 or 2
CAs are common, deeper chains are more rare and any number between 5
and 9 should suffice in practice. You can choose a lower number if,
for example, you trust certificates directly signed by an issuing CA
but not any CAs it delegates to. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_note_starttls_offer no

<p> Log the hostname of a remote SMTP server that offers STARTTLS,
when TLS is not already enabled for that server. </p>

<p> The logfile record looks like:  </p>

<pre>
postfix/smtp[pid]:  Host offered STARTTLS: [name.of.host]
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_cipherlist

<p> Obsolete Postfix &lt; 2.3 control for the Postfix SMTP client TLS
cipher list. As this feature applies to all TLS security levels, it is easy
to create inter-operability problems by choosing a non-default cipher
list. Do not use a non-default TLS cipher list on hosts that deliver email
to the public Internet: you will be unable to send email to servers that
only support the ciphers you exclude. Using a restricted cipher list
may be more appropriate for an internal MTA, where one can exert some
control over the TLS software and settings of the peer servers. </p>

<p> <b>Note:</b> do not use "" quotes around the parameter value. </p>

<p> This feature is available in Postfix version 2.2. It is not used with
Postfix 2.3 and later; use smtp_tls_mandatory_ciphers instead. </p>

%PARAM smtp_starttls_timeout 300s

<p> Time limit for Postfix SMTP client write and read operations
during TLS startup and shutdown handshake procedures. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_dkey_file $smtp_tls_dcert_file

<p> File with the Postfix SMTP client DSA private key in PEM format.
This file may be combined with the Postfix SMTP client DSA certificate
file specified with $smtp_tls_dcert_file. </p>

<p> The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account ("root"), and no access
to anyone else. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_tls_dcert_file

<p> File with the Postfix SMTP client DSA certificate in PEM format.
This file may also contain the Postfix SMTP client private DSA key. </p>

<p> See the discussion under smtp_tls_cert_file for more details.
</p>

<p> Example: </p>

<pre>
smtp_tls_dcert_file = /etc/postfix/client-dsa.pem
</pre>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM tls_append_default_CA no

<p> Append the system-supplied default certificate authority
certificates to the ones specified with *_tls_CApath or *_tls_CAfile.
The default is "no"; this prevents Postfix from trusting third-party
certificates and giving them relay permission with
permit_tls_all_clientcerts.  </p>

<p> This feature is available in Postfix 2.4.15, 2.5.11, 2.6.8,
2.7.2 and later versions. Specify "tls_append_default_CA = yes" for
backwards compatibility, to avoid breaking certificate verification
with sites that don't use permit_tls_all_clientcerts. </p>

%PARAM tls_random_exchange_name see "postconf -d" output

<p> Name of the pseudo random number generator (PRNG) state file
that is maintained by tlsmgr(8). The file is created when it does
not exist, and its length is fixed at 1024 bytes.  </p>

<p> As of version 2.5, Postfix no longer uses root privileges when
opening this file, and the default file location was changed from
${config_directory}/prng_exch to ${data_directory}/prng_exch.  As
a migration aid, an attempt to open the file under a non-Postfix
directory is redirected to the Postfix-owned data_directory, and a
warning is logged. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM tls_random_source see "postconf -d" output

<p> The external entropy source for the in-memory tlsmgr(8) pseudo
random number generator (PRNG) pool. Be sure to specify a non-blocking
source.  If this source is not a regular file, the entropy source
type must be prepended:  egd:/path/to/egd_socket for a source with
EGD compatible socket interface, or dev:/path/to/device for a
device file.  </p>

<p> Note: on OpenBSD systems specify /dev/arandom when /dev/urandom
gives timeout errors.  </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM tls_random_bytes 32

<p> The number of bytes that tlsmgr(8) reads from $tls_random_source
when (re)seeding the in-memory pseudo random number generator (PRNG)
pool. The default of 32 bytes (256 bits) is good enough for 128bit
symmetric keys.  If using EGD or a device file, a maximum of 255
bytes is read. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM tls_random_reseed_period 3600s

<p> The maximal time between attempts by tlsmgr(8) to re-seed the
in-memory pseudo random number generator (PRNG) pool from external
sources.  The actual time between re-seeding attempts is calculated
using the PRNG, and is between 0 and the time specified.  </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM tls_random_prng_update_period 3600s

<p> The time between attempts by tlsmgr(8) to save the state of
the pseudo random number generator (PRNG) to the file specified
with $tls_random_exchange_name.  </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM tls_daemon_random_bytes 32

<p> The number of pseudo-random bytes that an smtp(8) or smtpd(8)
process requests from the tlsmgr(8) server in order to seed its
internal pseudo random number generator (PRNG).  The default of 32
bytes (equivalent to 256 bits) is sufficient to generate a 128bit
(or 168bit) session key. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_sasl_tls_security_options $smtp_sasl_security_options

<p> The SASL authentication security options that the Postfix SMTP
client uses for TLS encrypted SMTP sessions. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtpd_sasl_tls_security_options $smtpd_sasl_security_options

<p> The SASL authentication security options that the Postfix SMTP
server uses for TLS encrypted SMTP sessions. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM smtp_generic_maps

<p> Optional lookup tables that perform address rewriting in the
SMTP client, typically to transform a locally valid address into
a globally valid address when sending mail across the Internet.
This is needed when the local machine does not have its own Internet
domain name, but uses something like <i>localdomain.local</i>
instead.  </p>

<p> The table format and lookups are documented in generic(5);
examples are shown in the ADDRESS_REWRITING_README and
STANDARD_CONFIGURATION_README documents. </p>

<p> This feature is available in Postfix 2.2 and later.  </p>

%PARAM message_reject_characters

<p> The set of characters that Postfix will reject in message
content.  The usual C-like escape sequences are recognized: <tt>\a
\b \f \n \r \t \v \<i>ddd</i></tt> (up to three octal digits) and
<tt>\\</tt>. </p>

<p> Example: </p>

<pre>
message_reject_characters = \0
</pre>

<p> This feature is available in Postfix 2.3 and later.  </p>

%PARAM message_strip_characters

<p> The set of characters that Postfix will remove from message
content.  The usual C-like escape sequences are recognized: <tt>\a
\b \f \n \r \t \v \<i>ddd</i></tt> (up to three octal digits) and
<tt>\\</tt>. </p>

<p> Example: </p>

<pre>
message_strip_characters = \0
</pre>

<p> This feature is available in Postfix 2.3 and later.  </p>

%PARAM frozen_delivered_to yes

<p> Update the local(8) delivery agent's idea of the Delivered-To:
address (see prepend_delivered_header) only once, at the start of
a delivery attempt; do not update the Delivered-To: address while
expanding aliases or .forward files. </p>

<p> This feature is available in Postfix 2.3 and later. With older
Postfix releases, the behavior is as if this parameter is set to
"no". The old setting can be expensive with deeply nested aliases
or .forward files. When an alias or .forward file changes the
Delivered-To: address, it ties up one queue file and one cleanup
process instance while mail is being forwarded.  </p>

%PARAM smtpd_peername_lookup yes

<p> Attempt to look up the remote SMTP client hostname, and verify that
the name matches the client IP address. A client name is set to
"unknown" when it cannot be looked up or verified, or when name
lookup is disabled.  Turning off name lookup reduces delays due to
DNS lookup and increases the maximal inbound delivery rate. </p>

<p> This feature is available in Postfix 2.3 and later.  </p>

%PARAM delay_logging_resolution_limit 2

<p> The maximal number of digits after the decimal point when logging
sub-second delay values.  Specify a number in the range 0..6.  </p>

<p> Large delay values are rounded off to an integral number seconds;
delay values below the delay_logging_resolution_limit are logged
as "0", and small delay values are logged with at most two-digit
precision.  </p>

<p> The format of the "delays=a/b/c/d" logging is as follows: </p>

<ul>

<li> a = time from message arrival to last active queue entry

<li> b = time from last active queue entry to connection setup

<li> c = time in connection setup, including DNS, EHLO and STARTTLS

<li> d = time in message transmission

</ul>

<p> This feature is available in Postfix 2.3 and later.  </p>

%PARAM bounce_template_file

<p> Pathname of a configuration file with bounce message templates.
These override the built-in templates of delivery status notification
(DSN) messages for undeliverable mail, for delayed mail, successful
delivery, or delivery verification. The bounce(5) manual page
describes how to edit and test template files.  </p>

<p> Template message body text may contain $name references to
Postfix configuration parameters. The result of $name expansion can
be previewed with "<b>postconf -b <i>file_name</i></b>" before the file
is placed into the Postfix configuration directory.  </p>

<p> This feature is available in Postfix 2.3 and later.  </p>

%PARAM sender_dependent_relayhost_maps

<p> A sender-dependent override for the global relayhost parameter
setting. The tables are searched by the envelope sender address and
@domain. A lookup result of DUNNO terminates the search without
overriding the global relayhost parameter setting (Postfix 2.6 and
later). This information is overruled with relay_transport,
sender_dependent_default_transport_maps, default_transport and with
the transport(5) table. </p>

<p> For safety reasons, this feature does not allow $number
substitutions in regular expression maps. </p>

<p>
This feature is available in Postfix 2.3 and later.
</p>

%PARAM empty_address_relayhost_maps_lookup_key &lt;&gt;

<p> The sender_dependent_relayhost_maps search string that will be
used instead of the null sender address. </p>

<p> This feature is available in Postfix 2.5 and later. With
earlier versions, sender_dependent_relayhost_maps lookups were
skipped for the null sender address.  </p>

%PARAM address_verify_sender_dependent_relayhost_maps $sender_dependent_relayhost_maps

<p>
Overrides the sender_dependent_relayhost_maps parameter setting for address
verification probes.
</p>

<p>
This feature is available in Postfix 2.3 and later.
</p>

%PARAM smtp_sender_dependent_authentication no

<p>
Enable sender-dependent authentication in the Postfix SMTP client; this is
available only with SASL authentication, and disables SMTP connection
caching to ensure that mail from different senders will use the
appropriate credentials.  </p>

<p>
This feature is available in Postfix 2.3 and later.
</p>

%PARAM lmtp_lhlo_name $myhostname

<p>
The hostname to send in the LMTP LHLO command.
</p>

<p>
The default value is the machine hostname.  Specify a hostname or
[ip.add.re.ss].
</p>

<p>
This information can be specified in the main.cf file for all LMTP
clients, or it can be specified in the master.cf file for a specific
client, for example:
</p>

<blockquote>
<pre>
/etc/postfix/master.cf:
    mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com
</pre>
</blockquote>

<p>
This feature is available in Postfix 2.3 and later.
</p>

%PARAM lmtp_discard_lhlo_keyword_address_maps

<p> Lookup tables, indexed by the remote LMTP server address, with
case insensitive lists of LHLO keywords (pipelining, starttls,
auth, etc.) that the LMTP client will ignore in the LHLO response
from a remote LMTP server. See lmtp_discard_lhlo_keywords for
details. The table is not indexed by hostname for consistency with
smtpd_discard_ehlo_keyword_address_maps. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_discard_lhlo_keywords

<p> A case insensitive list of LHLO keywords (pipelining, starttls,
auth, etc.) that the LMTP client will ignore in the LHLO response
from a remote LMTP server. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

<p> Notes: </p>

<ul>

<li> <p> Specify the <b>silent-discard</b> pseudo keyword to prevent
this action from being logged. </p>

<li> <p> Use the lmtp_discard_lhlo_keyword_address_maps feature to
discard LHLO keywords selectively. </p>

</ul>

%PARAM lmtp_lhlo_timeout 300s

<p> The LMTP client time limit for sending the LHLO command, and
for receiving the initial server response. </p>

<p> Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks).  The default time unit is s (seconds).  </p>

%PARAM lmtp_sasl_tls_security_options $lmtp_sasl_security_options

<p> The LMTP-specific version of the smtp_sasl_tls_security_options
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_sasl_mechanism_filter

<p> The LMTP-specific version of the smtp_sasl_mechanism_filter
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_bind_address

<p> The LMTP-specific version of the smtp_bind_address configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_bind_address6

<p> The LMTP-specific version of the smtp_bind_address6 configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_host_lookup dns

<p> The LMTP-specific version of the smtp_host_lookup configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_connection_cache_destinations

<p> The LMTP-specific version of the smtp_connection_cache_destinations
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_per_site

<p> The LMTP-specific version of the smtp_tls_per_site configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_generic_maps

<p> The LMTP-specific version of the smtp_generic_maps configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_pix_workaround_threshold_time 500s

<p> The LMTP-specific version of the smtp_pix_workaround_threshold_time
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_pix_workaround_delay_time 10s

<p> The LMTP-specific version of the smtp_pix_workaround_delay_time
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_connection_reuse_time_limit 300s

<p> The LMTP-specific version of the smtp_connection_reuse_time_limit
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_starttls_timeout 300s

<p> The LMTP-specific version of the smtp_starttls_timeout configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_line_length_limit 990

<p> The LMTP-specific version of the smtp_line_length_limit
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_mx_address_limit 5

<p> The LMTP-specific version of the smtp_mx_address_limit configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_mx_session_limit 2

<p> The LMTP-specific version of the smtp_mx_session_limit configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_scert_verifydepth 9

<p> The LMTP-specific version of the smtp_tls_scert_verifydepth
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_skip_5xx_greeting yes

<p> The LMTP-specific version of the smtp_skip_5xx_greeting
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_randomize_addresses yes

<p> The LMTP-specific version of the smtp_randomize_addresses
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_quote_rfc821_envelope yes

<p> The LMTP-specific version of the smtp_quote_rfc821_envelope
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_defer_if_no_mx_address_found no

<p> The LMTP-specific version of the smtp_defer_if_no_mx_address_found
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_connection_cache_on_demand yes

<p> The LMTP-specific version of the smtp_connection_cache_on_demand
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_use_tls no

<p> The LMTP-specific version of the smtp_use_tls configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_enforce_tls no

<p> The LMTP-specific version of the smtp_enforce_tls configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_security_level

<p> The LMTP-specific version of the smtp_tls_security_level configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_enforce_peername yes

<p> The LMTP-specific version of the smtp_tls_enforce_peername
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_note_starttls_offer no

<p> The LMTP-specific version of the smtp_tls_note_starttls_offer
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_sender_dependent_authentication no

<p> The LMTP-specific version of the smtp_sender_dependent_authentication
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM connection_cache_protocol_timeout 5s

<p> Time limit for connection cache connect, send or receive
operations.  The time limit is enforced in the client. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_sasl_type cyrus

<p> The SASL plug-in type that the Postfix SMTP server should use
for authentication. The available types are listed with the
"<b>postconf -a</b>" command. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_sasl_type cyrus

<p> The SASL plug-in type that the Postfix SMTP client should use
for authentication.  The available types are listed with the
"<b>postconf -A</b>" command. </p>

<p> This feature is available in Postfix 2.3 and later. </p>


%PARAM lmtp_sasl_type cyrus

<p> The SASL plug-in type that the Postfix LMTP client should use
for authentication.  The available types are listed with the
"<b>postconf -A</b>" command. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_sasl_path smtpd

<p> Implementation-specific information that the Postfix SMTP server
passes through to
the SASL plug-in implementation that is selected with
<b>smtpd_sasl_type</b>.  Typically this specifies the name of a
configuration file or rendezvous point. </p>

<p> This feature is available in Postfix 2.3 and later. In earlier
releases it was called <b>smtpd_sasl_application_name</b>. </p>

%PARAM cyrus_sasl_config_path

<p> Search path for Cyrus SASL application configuration files,
currently used only to locate the $smtpd_sasl_path.conf file.
Specify zero or more directories separated by a colon character,
or an empty value to use Cyrus SASL's built-in search path.  </p>

<p> This feature is available in Postfix 2.5 and later when compiled
with Cyrus SASL 2.1.22 or later. </p>

%PARAM smtp_sasl_path

<p> Implementation-specific information that the Postfix SMTP client
passes through to
the SASL plug-in implementation that is selected with
<b>smtp_sasl_type</b>.  Typically this specifies the name of a
configuration file or rendezvous point. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_sasl_path

<p> Implementation-specific information that is passed through to
the SASL plug-in implementation that is selected with
<b>lmtp_sasl_type</b>.  Typically this specifies the name of a
configuration file or rendezvous point. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM plaintext_reject_code 450

<p>
The numerical Postfix SMTP server response code when a request
is rejected by the <b>reject_plaintext_session</b> restriction.
</p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM resolve_numeric_domain no

<p> Resolve "user@ipaddress" as "user@[ipaddress]", instead of
rejecting the address as invalid.  </p>

<p> This feature is available in Postfix 2.3 and later.

%PARAM mailbox_transport_maps

<p> Optional lookup tables with per-recipient message delivery
transports to use for local(8) mailbox delivery, whether or not the
recipients are found in the UNIX passwd database. </p>

<p> The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.  </p>

<p> For safety reasons, this feature does not allow $number
substitutions in regular expression maps. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM fallback_transport_maps

<p> Optional lookup tables with per-recipient message delivery
transports for recipients that the local(8) delivery agent could
not find in the aliases(5) or UNIX password database. </p>

<p> The precedence of local(8) delivery features from high to low
is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
fallback_transport_maps, fallback_transport and luser_relay.  </p>

<p> For safety reasons, this feature does not allow $number
substitutions in regular expression maps. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_cname_overrides_servername version dependent

<p> Allow DNS CNAME records to override the servername that the
Postfix SMTP client uses for logging, SASL password lookup, TLS
policy decisions, or TLS certificate verification. The value "no"
hardens Postfix smtp_tls_per_site hostname-based policies against
false hostname information in DNS CNAME records, and makes SASL
password file lookups more predictable. This is the default setting
as of Postfix 2.3. </p>

<p> This feature is available in Postfix 2.2.9 and later. </p>

%PARAM lmtp_cname_overrides_servername yes

<p> The LMTP-specific version of the smtp_cname_overrides_servername
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_sasl_tls_verified_security_options $smtp_sasl_tls_security_options

<p> The SASL authentication security options that the Postfix SMTP
client uses for TLS encrypted SMTP sessions with a verified server
certificate. </p>

<p> When mail is sent to the public MX host for the recipient's
domain, server certificates are by default optional, and delivery
proceeds even if certificate verification fails. For delivery via
a submission service that requires SASL authentication, it may be
appropriate to send plaintext passwords only when the connection
to the server is strongly encrypted <b>and</b> the server identity
is verified. </p>

<p> The smtp_sasl_tls_verified_security_options parameter makes it
possible to only enable plaintext mechanisms when a secure connection
to the server is available. Submission servers subject to this
policy must either have verifiable certificates or offer suitable
non-plaintext SASL mechanisms. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM lmtp_sasl_tls_verified_security_options $lmtp_sasl_tls_security_options

<p> The LMTP-specific version of the
smtp_sasl_tls_verified_security_options configuration parameter.
See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_connection_cache_time_limit 2s

<p> The LMTP-specific version of the
smtp_connection_cache_time_limit configuration parameter.
See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_delay_open_until_valid_rcpt yes

<p> Postpone the start of an SMTP mail transaction until a valid
RCPT TO command is received. Specify "no" to create a mail transaction
as soon as the SMTP server receives a valid MAIL FROM command. </p>

<p> With sites that reject lots of mail, the default setting reduces
the use of
disk, CPU and memory resources. The downside is that rejected
recipients are logged with NOQUEUE instead of a mail transaction
ID. This complicates the logfile analysis of multi-recipient mail.
</p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_cert_file

<p> The LMTP-specific version of the smtp_tls_cert_file
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_key_file $lmtp_tls_cert_file

<p> The LMTP-specific version of the smtp_tls_key_file
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_dcert_file

<p> The LMTP-specific version of the smtp_tls_dcert_file
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_dkey_file $lmtp_tls_dcert_file

<p> The LMTP-specific version of the smtp_tls_dkey_file
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_CAfile

<p> The LMTP-specific version of the smtp_tls_CAfile
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_CApath

<p> The LMTP-specific version of the smtp_tls_CApath
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_loglevel 0

<p> The LMTP-specific version of the smtp_tls_loglevel
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_session_cache_database

<p> The LMTP-specific version of the smtp_tls_session_cache_database
configuration parameter. See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_session_cache_timeout  3600s

<p> The LMTP-specific version of the smtp_tls_session_cache_timeout
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_tls_policy_maps

<p> Optional lookup tables with the Postfix SMTP client TLS security
policy by next-hop destination; when a non-empty value is specified,
this overrides the obsolete smtp_tls_per_site parameter.  See
TLS_README for a more detailed discussion of TLS security levels.
</p>

<p> The TLS policy table is indexed by the full next-hop destination,
which is either the recipient domain, or the verbatim next-hop
specified in the transport table, $local_transport, $virtual_transport,
$relay_transport or $default_transport. This includes any enclosing
square brackets and any non-default destination server port suffix. The
LMTP socket type prefix (inet: or unix:) is not included in the lookup
key. </p>

<p> Only the next-hop domain, or $myhostname with LMTP over UNIX-domain
sockets, is used as the nexthop name for certificate verification. The
port and any enclosing square brackets are used in the table lookup key,
but are not used for server name verification. </p>

<p> When the lookup key is a domain name without enclosing square brackets
or any <i>:port</i> suffix (typically the recipient domain), and the full
domain is not found in the table, just as with the transport(5) table,
the parent domain starting with a leading "." is matched recursively. This
allows one to specify a security policy for a recipient domain and all
its sub-domains. </p>

<p> The lookup result is a security level, followed by an optional list
of whitespace and/or comma separated name=value attributes that override
related main.cf settings. The TLS security levels in order of increasing
security are: </p>

<dl>

<dt><b>none</b></dt>
<dd>No TLS. No additional attributes are supported at this level. </dd>

<dt><b>may</b></dt>
<dd>Opportunistic TLS. Since sending in the clear is acceptable,
demanding stronger than default TLS security merely reduces
inter-operability. The optional "ciphers", "exclude" and "protocols"
attributes (available for opportunistic TLS with Postfix &ge; 2.6)
override the "smtp_tls_ciphers", "smtp_tls_exclude_ciphers" and
"smtp_tls_protocols" configuration parameters. When opportunistic TLS
handshakes fail, Postfix retries the connection with TLS disabled.
This allows mail delivery to sites with non-interoperable TLS
implementations.</dd>

<dt><b>encrypt</b></dt> <dd>Mandatory TLS encryption. At this level
and higher, the optional "protocols" attribute overrides the main.cf
smtp_tls_mandatory_protocols parameter, the optional "ciphers" attribute
overrides the main.cf smtp_tls_mandatory_ciphers parameter, and the
optional "exclude" attribute (Postfix &ge; 2.6) overrides the main.cf
smtp_tls_mandatory_exclude_ciphers parameter. In the policy table,
multiple protocols or excluded ciphers must be separated by colons,
as attribute values may not contain whitespace or commas. </dd>

<dt><b>fingerprint</b></dt> <dd>Certificate fingerprint
verification. Available with Postfix 2.5 and later. At this security
level, there are no trusted certificate authorities. The certificate
trust chain, expiration date, ... are not checked. Instead,
the optional <b>match</b> attribute, or else the main.cf
<b>smtp_tls_fingerprint_cert_match</b> parameter, lists the
valid "fingerprints" of the server certificate. The digest
algorithm used to calculate the fingerprint is selected by the
<b>smtp_tls_fingerprint_digest</b> parameter. Multiple fingerprints can
be combined with a "|" delimiter in a single match attribute, or multiple
match attributes can be employed. The ":" character is not used as a
delimiter as it occurs between each pair of fingerprint (hexadecimal)
digits. </dd>

<dt><b>verify</b></dt> <dd>Mandatory TLS verification.  At this security
level, DNS MX lookups are trusted to be secure enough, and the name
verified in the server certificate is usually obtained indirectly via
unauthenticated DNS MX lookups.  The optional "match" attribute overrides
the main.cf smtp_tls_verify_cert_match parameter. In the policy table,
multiple match patterns and strategies must be separated by colons.
In practice explicit control over matching is more common with the
"secure" policy, described below. </dd>

<dt><b>secure</b></dt> <dd>Secure-channel TLS. At this security level, DNS
MX lookups, though potentially used to determine the candidate next-hop
gateway IP addresses, are <b>not</b> trusted to be secure enough for TLS
peername verification. Instead, the default name verified in the server
certificate is obtained directly from the next-hop, or is explicitly
specified via the optional <b>match</b> attribute which overrides the
main.cf smtp_tls_secure_cert_match parameter. In the policy table,
multiple match patterns and strategies must be separated by colons.
The match attribute is most useful when multiple domains are supported by
common server, the policy entries for additional domains specify matching
rules for the primary domain certificate. While transport table overrides
routing the secondary domains to the primary nexthop also allow secure
verification, they risk delivery to the wrong destination when domains
change hands or are re-assigned to new gateways. With the "match"
attribute approach, routing is not perturbed, and mail is deferred if
verification of a new MX host fails. </dd>

</dl>

<p>
Example:
</p>

<pre>
/etc/postfix/main.cf:
    smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
    # Postfix 2.5 and later
    smtp_tls_fingerprint_digest = md5
</pre>

<pre>
/etc/postfix/tls_policy:
    example.edu                 none
    example.mil                 may
    example.gov                 encrypt protocols=TLSv1
    example.com                 verify ciphers=high
    example.net                 secure
    .example.net                secure match=.example.net:example.net
    [mail.example.org]:587      secure match=nexthop
    # Postfix 2.5 and later
    [thumb.example.org]          fingerprint
    	match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
	match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
</pre>

<p> <b>Note:</b> The <b>hostname</b> strategy if listed in a non-default
setting of smtp_tls_secure_cert_match or in the <b>match</b> attribute
in the policy table can render the <b>secure</b> level vulnerable to
DNS forgery. Do not use the <b>hostname</b> strategy for secure-channel
configurations in environments where DNS security is not assured. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_tls_mandatory_protocols SSLv3, TLSv1

<p> List of SSL/TLS protocols that the Postfix SMTP client will use with
mandatory TLS encryption.  In main.cf the values are separated by
whitespace, commas or colons. In the policy table "protocols" attribute
(see smtp_tls_policy_maps) the only valid separator is colon. An
empty value means allow all protocols. The valid protocol names, (see
<b>SSL_get_version(3)</b>), are "SSLv2", "SSLv3" and "TLSv1". </p>

<p> With Postfix &ge; 2.5 the parameter syntax is expanded to support
protocol exclusions. One can now explicitly exclude SSLv2 by setting
"smtp_tls_mandatory_protocols = !SSLv2". To exclude both SSLv2 and
SSLv3 set "smtp_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing
the protocols to include, rather than protocols to exclude, is still
supported; use the form you find more intuitive. </p>

<p> Since SSL version 2 has known protocol weaknesses and is now
deprecated, the default setting excludes "SSLv2".  This means that by
default, SSL version 2 will not be used at the "encrypt" security level
and higher. </p>

<p> See the documentation of the smtp_tls_policy_maps parameter and
TLS_README for more information about security levels. </p>

<p> Example: </p>

<pre>
smtp_tls_mandatory_protocols = TLSv1
# Alternative form with Postfix &ge; 2.5:
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
</pre>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_tls_verify_cert_match hostname

<p> The server certificate peername verification method for the
"verify" TLS security level. In a "verify" TLS policy table
($smtp_tls_policy_maps) entry the optional "match" attribute
overrides this main.cf setting. </p>

<p> This parameter specifies one or more patterns or strategies separated
by commas, whitespace or colons.  In the policy table the only valid
separator is the colon character. </p>

<p> Patterns specify domain names, or domain name suffixes: </p>

<dl>

<dt><i>example.com</i></dt> <dd> Match the <i>example.com</i> domain,
i.e. one of the names the server certificate must be <i>example.com</i>,
upper and lower case distinctions are ignored. </dd>

<dt><i>.example.com</i></dt>
<dd> Match subdomains of the <i>example.com</i> domain, i.e. match
a name in the server certificate that consists of a non-zero number of
labels followed by a <i>.example.com</i> suffix. Case distinctions are
ignored.</dd>

</dl>

<p> Strategies specify a transformation from the next-hop domain
to the expected name in the server certificate: </p>

<dl>

<dt>nexthop</dt>
<dd> Match against the next-hop domain, which is either the recipient
domain, or the transport next-hop configured for the domain stripped of
any optional socket type prefix, enclosing square brackets and trailing
port. When MX lookups are not suppressed, this is the original nexthop
domain prior to the MX lookup, not the result of the MX lookup. For
LMTP delivery via UNIX-domain sockets, the verified next-hop name is
$myhostname.  This strategy is suitable for use with the "secure"
policy. Case is ignored.</dd>

<dt>dot-nexthop</dt>
<dd> As above, but match server certificate names that are subdomains
of the next-hop domain. Case is ignored.</dd>

<dt>hostname</dt> <dd> Match against the hostname of the server, often
obtained via an unauthenticated DNS MX lookup. For LMTP delivery via
UNIX-domain sockets, the verified name is $myhostname. This matches
the verification strategy of the "MUST" keyword in the obsolete
smtp_tls_per_site table, and is suitable for use with the "verify"
security level. When the next-hop name is enclosed in square brackets
to suppress MX lookups, the "hostname" strategy is the same as the
"nexthop" strategy. Case is ignored.</dd>

</dl>

<p>
Sample main.cf setting:
</p>

<pre>
smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop
</pre>

<p>
Sample policy table override:
</p>

<pre>
example.com     verify  match=hostname:nexthop
.example.com    verify  match=example.com:.example.com:hostname
</pre>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_tls_secure_cert_match nexthop, dot-nexthop

<p> The server certificate peername verification method for the
"secure" TLS security level. In a "secure" TLS policy table
($smtp_tls_policy_maps) entry the optional "match" attribute
overrides this main.cf setting. </p>

<p> This parameter specifies one or more patterns or strategies separated
by commas, whitespace or colons.  In the policy table the only valid
separator is the colon character. </p>

<p> For a description of the pattern and strategy syntax see the
smtp_tls_verify_cert_match parameter. The "hostname" strategy should
be avoided in this context, as in the absence of a secure global DNS, using
the results of MX lookups in certificate verification is not immune to active
(man-in-the-middle) attacks on DNS. </p>

<p>
Sample main.cf setting:
</p>

<blockquote>
<pre>
smtp_tls_secure_cert_match = nexthop
</pre>
</blockquote>

<p>
Sample policy table override:
</p>

<blockquote>
<pre>
example.net     secure match=example.com:.example.com
.example.net    secure match=example.com:.example.com
</pre>
</blockquote>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_policy_maps

<p> The LMTP-specific version of the smtp_tls_policy_maps
configuration parameter. See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_mandatory_protocols SSLv3, TLSv1

<p> The LMTP-specific version of the smtp_tls_mandatory_protocols
configuration parameter. See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_verify_cert_match hostname

<p> The LMTP-specific version of the smtp_tls_verify_cert_match
configuration parameter. See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_secure_cert_match nexthop

<p> The LMTP-specific version of the smtp_tls_secure_cert_match
configuration parameter. See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_tls_mandatory_protocols SSLv3, TLSv1

<p> The SSL/TLS protocols accepted by the Postfix SMTP server with
mandatory TLS encryption. If the list is empty, the server supports all
available SSL/TLS protocol versions.  A non-empty value is a list
of protocol
names separated by whitespace, commas or colons. The supported protocol
names are "SSLv2", "SSLv3" and "TLSv1", and are not case sensitive. </p>

<p> With Postfix &ge; 2.5 the parameter syntax is expanded to support
protocol exclusions. One can now explicitly exclude SSLv2 by setting
"smtpd_tls_mandatory_protocols = !SSLv2". To exclude both SSLv2 and
SSLv3 set "smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing
the protocols to include, rather than protocols to exclude, is still
supported, use the form you find more intuitive. </p>

<p> Since SSL version 2 has known protocol weaknesses and is now
deprecated, the default setting excludes "SSLv2".  This means that
by default, SSL version 2 will not be used at the "encrypt" security
level. </p>

<p> Example: </p>

<pre>
smtpd_tls_mandatory_protocols = TLSv1
# Alternative form with Postfix &ge; 2.5:
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
</pre>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_tls_security_level

<p> The default SMTP TLS security level for the Postfix SMTP client;
when a non-empty value is specified, this overrides the obsolete
parameters smtp_use_tls, smtp_enforce_tls, and smtp_tls_enforce_peername.
</p>

<p> Specify one of the following security levels: </p>

<dl>

<dt><b>none</b></dt> <dd> TLS will not be used unless enabled for specific
destinations via smtp_tls_policy_maps. </dd>

<dt><b>may</b></dt>
<dd> Opportunistic TLS. Use TLS if this is supported by the remote
SMTP server, otherwise use plaintext. Since
sending in the clear is acceptable, demanding stronger than default TLS
security merely reduces inter-operability.
The "smtp_tls_ciphers" and "smtp_tls_protocols" (Postfix &ge; 2.6)
configuration parameters provide control over the protocols and
cipher grade used with opportunistic TLS.  With earlier releases the
opportunistic TLS cipher grade is always "export" and no protocols
are disabled.
When TLS handshakes fail, the connection is retried with TLS disabled.
This allows mail delivery to sites with non-interoperable TLS
implementations. </dd>

<dt><b>encrypt</b></dt> <dd>Mandatory TLS encryption. Since a minimum
level of security is intended, it is reasonable to be specific about
sufficiently secure protocol versions and ciphers. At this security level
and higher, the main.cf parameters smtp_tls_mandatory_protocols and
smtp_tls_mandatory_ciphers specify the TLS protocols and minimum
cipher grade which the administrator considers secure enough for
mandatory encrypted sessions. This security level is not an appropriate
default for systems delivering mail to the Internet. </dd>

<dt><b>fingerprint</b></dt> <dd>Certificate fingerprint
verification. Available with Postfix 2.5 and later. At this security
level, there are no trusted certificate authorities. The certificate
trust chain, expiration date, ... are not checked. Instead,
the <b>smtp_tls_fingerprint_cert_match</b> parameter lists
the valid "fingerprints" of the server certificate. The digest
algorithm used to calculate the fingerprint is selected by the
<b>smtp_tls_fingerprint_digest</b> parameter. </dd>

<dt><b>verify</b></dt> <dd>Mandatory TLS verification. At this security
level, DNS MX lookups are trusted to be secure enough, and the name
verified in the server certificate is usually obtained indirectly
via unauthenticated DNS MX lookups. The smtp_tls_verify_cert_match
parameter controls how the server name is verified. In practice explicit
control over matching is more common at the "secure" level, described
below. This security level is not an appropriate default for systems
delivering mail to the Internet. </dd>

<dt><b>secure</b></dt> <dd>Secure-channel TLS.  At this security level,
DNS MX lookups, though potentially used to determine the candidate
next-hop gateway IP addresses, are <b>not</b> trusted to be secure enough
for TLS peername verification. Instead, the default name verified in
the server certificate is obtained from the next-hop domain as specified
in the smtp_tls_secure_cert_match configuration parameter. The default
matching rule is that a server certificate matches when its name is equal
to or is a sub-domain of the nexthop domain. This security level is not
an appropriate default for systems delivering mail to the Internet. </dd>

</dl>

<p>
Examples:
</p>

<pre>
# No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
smtp_tls_security_level = none
</pre>

<pre>
# Opportunistic TLS.
smtp_tls_security_level = may
# Postfix &ge; 2.6:
# Do not tweak opportunistic ciphers or protocol unless it is essential
# to do so (if a security vulnerability is found in the SSL library that
# can be mitigated by disabling a particular protocol or raising the
# cipher grade from "export" to "low" or "medium").
smtp_tls_ciphers = export
smtp_tls_protocols = !SSLv2
</pre>

<pre>
# Mandatory (high-grade) TLS encryption.
smtp_tls_security_level = encrypt
smtp_tls_mandatory_ciphers = high
</pre>

<pre>
# Mandatory TLS verification of hostname or nexthop domain.
smtp_tls_security_level = verify
smtp_tls_mandatory_ciphers = high
smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop
</pre>

<pre>
# Secure channel TLS with exact nexthop name match.
smtp_tls_security_level = secure
smtp_tls_mandatory_protocols = TLSv1
smtp_tls_mandatory_ciphers = high
smtp_tls_secure_cert_match = nexthop
</pre>

<pre>
# Certificate fingerprint verification (Postfix &ge; 2.5).
# The CA-less "fingerprint" security level only scales to a limited
# number of destinations. As a global default rather than a per-site
# setting, this is practical when mail for all recipients is sent
# to a central mail hub.
relayhost = [mailhub.example.com]
smtp_tls_security_level = fingerprint
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
smtp_tls_mandatory_ciphers = high
smtp_tls_fingerprint_cert_match =
    3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
    EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
</pre>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_milters

<p> A list of Milter (mail filter) applications for new mail that
arrives via the Postfix smtpd(8) server.  See the MILTER_README
document for details.  </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM non_smtpd_milters

<p> A list of Milter (mail filter) applications for new mail that
does not arrive via the Postfix smtpd(8) server. This includes local
submission via the sendmail(1) command line, new mail that arrives
via the Postfix qmqpd(8) server, and old mail that is re-injected
into the queue with "postsuper -r".  See the MILTER_README document
for details.  </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_protocol 6

<p> The mail filter protocol version and optional protocol extensions
for communication with a Milter application; prior to Postfix 2.6
the default protocol is 2. Postfix
sends this version number during the initial protocol handshake.
It should match the version number that is expected by the mail
filter application (or by its Milter library).  </p>

<p>Protocol versions: </p>

<dl compact>

<dt>2</dt> <dd>Use Sendmail 8 mail filter protocol version 2 (default
with Sendmail version 8.11 .. 8.13 and Postfix version 2.3 ..
2.5).</dd>

<dt>3</dt> <dd>Use Sendmail 8 mail filter protocol version 3.</dd>

<dt>4</dt> <dd>Use Sendmail 8 mail filter protocol version 4.</dd>

<dt>6</dt> <dd>Use Sendmail 8 mail filter protocol version 6 (default
with Sendmail version 8.14 and Postfix version 2.6).</dd>

</dl>

<p>Protocol extensions: </p>

<dl compact>

<dt>no_header_reply</dt> <dd> Specify this when the Milter application
will not reply for each individual message header.</dd>

</dl>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_default_action tempfail

<p> The default action when a Milter (mail filter) application is
unavailable or mis-configured. Specify one of the following: </p>

<dl compact>

<dt>accept</dt> <dd>Proceed as if the mail filter was not present.
</dd>

<dt>reject</dt> <dd>Reject all further commands in this session
with a permanent status code.</dd>

<dt>tempfail</dt> <dd>Reject all further commands in this session
with a temporary status code. </dd>

<dt>quarantine</dt> <dd>Like "accept", but freeze the message in
the "hold" queue. Available with Postfix 2.6 and later. </dd>

</dl>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_connect_timeout 30s

<p> The time limit for connecting to a Milter (mail filter)
application, and for negotiating protocol options. </p>

<p> Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). </p>

<p> Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks). The default time unit is s (seconds). </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_command_timeout 30s

<p> The time limit for sending an SMTP command to a Milter (mail
filter) application, and for receiving the response.  </p>

<p> Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). </p>

<p> Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks). The default time unit is s (seconds). </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_content_timeout 300s

<p> The time limit for sending message content to a Milter (mail
filter) application, and for receiving the response.  </p>

<p> Specify a non-zero time value (an integral value plus an optional
one-letter suffix that specifies the time unit). </p>

<p> Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks). The default time unit is s (seconds). </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_connect_macros see "postconf -d" output

<p> The macros that are sent to Milter (mail filter) applications
after completion of an SMTP connection. See MILTER_README
for a list of available macro names and their meanings. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_helo_macros see "postconf -d" output

<p> The macros that are sent to Milter (mail filter) applications
after the SMTP HELO or EHLO command. See
MILTER_README for a list of available macro names and their meanings.
</p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_mail_macros see "postconf -d" output

<p> The macros that are sent to Milter (mail filter) applications
after the SMTP MAIL FROM command. See MILTER_README
for a list of available macro names and their meanings. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_rcpt_macros see "postconf -d" output

<p> The macros that are sent to Milter (mail filter) applications
after the SMTP RCPT TO command. See MILTER_README
for a list of available macro names and their meanings. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_data_macros see "postconf -d" output

<p> The macros that are sent to version 4 or higher Milter (mail
filter) applications after the SMTP DATA command. See MILTER_README
for a list of available macro names and their meanings.  </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_end_of_header_macros see "postconf -d" output

<p> The macros that are sent to Milter (mail filter) applications
after the end of the message header. See MILTER_README for a list
of available macro names and their meanings.  </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM milter_end_of_data_macros see "postconf -d" output

<p> The macros that are sent to Milter (mail filter) applications
after the message end-of-data. See MILTER_README for a list of
available macro names and their meanings.  </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_unknown_command_macros see "postconf -d" output

<p> The macros that are sent to version 3 or higher Milter (mail
filter) applications after an unknown SMTP command.  See MILTER_README
for a list of available macro names and their meanings.  </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_macro_daemon_name $myhostname

<p> The {daemon_name} macro value for Milter (mail filter) applications.
See MILTER_README for a list of available macro names and their
meanings.  </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM milter_macro_v $mail_name $mail_version

<p> The {v} macro value for Milter (mail filter) applications.
See MILTER_README for a list of available macro names and their
meanings.  </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_tls_mandatory_ciphers medium

<p> The minimum TLS cipher grade that the Postfix SMTP server will
use with mandatory TLS encryption. The default grade ("medium") is
sufficiently strong that any benefit from globally restricting TLS
sessions to a more stringent grade is likely negligible, especially
given the fact that many implementations still do not offer any stronger
("high" grade) ciphers, while those that do, will always use "high"
grade ciphers. So insisting on "high" grade ciphers is generally
counter-productive. Allowing "export" or "low" ciphers is typically
not a good idea, as systems limited to just these are limited to
obsolete browsers. No known SMTP clients fail to support at least
one "medium" or "high" grade cipher. </p>

<p> The following cipher grades are supported: </p>

<dl>
<dt><b>export</b></dt>
<dd> Enable "EXPORT" grade or stronger OpenSSL ciphers.
This is the most appropriate setting for public MX hosts, and is always
used with opportunistic TLS encryption. The underlying cipherlist
is specified via the tls_export_cipherlist configuration parameter,
which you are strongly encouraged to not change. </dd>

<dt><b>low</b></dt>
<dd> Enable "LOW" grade or stronger OpenSSL ciphers. The
underlying cipherlist is specified via the tls_low_cipherlist
configuration parameter, which you are strongly encouraged to
not change. </dd>

<dt><b>medium</b></dt>
<dd> Enable "MEDIUM" grade or stronger OpenSSL ciphers. These use 128-bit
or longer symmetric bulk-encryption keys. This is the default minimum
strength for mandatory TLS encryption. The underlying cipherlist is
specified via the tls_medium_cipherlist configuration parameter, which
you are strongly encouraged to not change. </dd>

<dt><b>high</b></dt>
<dd> Enable only "HIGH" grade OpenSSL ciphers. The
underlying cipherlist is specified via the tls_high_cipherlist
configuration parameter, which you are strongly encouraged to
not change. </dd>

<dt><b>null</b></dt>
<dd> Enable only the "NULL" OpenSSL ciphers, these provide authentication
without encryption.  This setting is only appropriate in the rare
case that all clients are prepared to use NULL ciphers (not normally
enabled in TLS clients). The underlying cipherlist is specified via the
tls_null_cipherlist configuration parameter, which you are strongly
encouraged to not change. </dd>

</dl>

<p> Cipher types listed in
smtpd_tls_mandatory_exclude_ciphers or smtpd_tls_exclude_ciphers are
excluded from the base definition of the selected cipher grade. See
smtpd_tls_ciphers for cipher controls that apply to opportunistic
TLS. </p>

<p> The underlying cipherlists for grades other than "null" include
anonymous ciphers, but these are automatically filtered out if the
server is configured to ask for client certificates.  You are very
unlikely to need to take any steps to exclude anonymous ciphers, they
are excluded automatically as required.  If you must exclude anonymous
ciphers even when Postfix does not need or use peer certificates, set
"smtpd_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers only
when TLS is enforced, set "smtpd_tls_mandatory_exclude_ciphers = aNULL". </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_tls_exclude_ciphers

<p> List of ciphers or cipher types to exclude from the SMTP server
cipher list at all TLS security levels. Excluding valid ciphers
can create interoperability problems. DO NOT exclude ciphers unless it
is essential to do so. This is not an OpenSSL cipherlist; it is a simple
list separated by whitespace and/or commas. The elements are a single
cipher, or one or more "+" separated cipher properties, in which case
only ciphers matching <b>all</b> the properties are excluded. </p>

<p> Examples (some of these will cause problems): </p>

<blockquote>
<pre>
smtpd_tls_exclude_ciphers = aNULL
smtpd_tls_exclude_ciphers = MD5, DES
smtpd_tls_exclude_ciphers = DES+MD5
smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
smtpd_tls_exclude_ciphers = kEDH+aRSA
</pre>
</blockquote>

<p> The first setting disables anonymous ciphers. The next setting
disables ciphers that use the MD5 digest algorithm or the (single) DES
encryption algorithm. The next setting disables ciphers that use MD5 and
DES together.  The next setting disables the two ciphers "AES256-SHA"
and "DES-CBC3-MD5". The last setting disables ciphers that use "EDH"
key exchange with RSA authentication. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_tls_mandatory_exclude_ciphers

<p> Additional list of ciphers or cipher types to exclude from the
SMTP server cipher list at mandatory TLS security levels. This list
works in addition to the exclusions listed with smtpd_tls_exclude_ciphers
(see there for syntax details).  </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_tls_mandatory_ciphers medium

<p> The minimum TLS cipher grade that the Postfix SMTP client will
use with
mandatory TLS encryption.  The default value "medium" is suitable
for most destinations with which you may want to enforce TLS, and
is beyond the reach of today's cryptanalytic methods. See
smtp_tls_policy_maps for information on how to configure ciphers
on a per-destination basis. </p>

<p> The following cipher grades are supported: </p>

<dl>
<dt><b>export</b></dt>
<dd> Enable "EXPORT" grade or better OpenSSL
ciphers.  This is the default for opportunistic encryption. It is
not recommended for mandatory encryption unless you must enforce TLS
with "crippled" peers. The underlying cipherlist is specified via the
tls_export_cipherlist configuration parameter, which you are strongly
encouraged to not change. </dd>

<dt><b>low</b></dt>
<dd> Enable "LOW" grade or better OpenSSL ciphers.  This
setting is only appropriate for internal mail servers.  The underlying
cipherlist is specified via the tls_low_cipherlist configuration
parameter, which you are strongly encouraged to not change. </dd>

<dt><b>medium</b></dt>
<dd> Enable "MEDIUM" grade or better OpenSSL ciphers.
The underlying cipherlist is specified via the tls_medium_cipherlist
configuration parameter, which you are strongly encouraged to not change.
</dd>

<dt><b>high</b></dt>
<dd> Enable only "HIGH" grade OpenSSL ciphers.  This setting may
be appropriate when all mandatory TLS destinations (e.g. when all
mail is routed to a suitably capable relayhost) support at least one
"HIGH" grade cipher. The underlying cipherlist is specified via the
tls_high_cipherlist configuration parameter, which you are strongly
encouraged to not change. </dd>

<dt><b>null</b></dt>
<dd> Enable only the "NULL" OpenSSL ciphers, these provide authentication
without encryption.  This setting is only appropriate in the rare case
that all servers are prepared to use NULL ciphers (not normally enabled
in TLS servers). A plausible use-case is an LMTP server listening on a
UNIX-domain socket that is configured to support "NULL" ciphers. The
underlying cipherlist is specified via the tls_null_cipherlist
configuration parameter, which you are strongly encouraged to not
change. </dd>

</dl>

<p> The underlying cipherlists for grades other than "null" include
anonymous ciphers, but these are automatically filtered out if the
Postfix SMTP client is configured to verify server certificates.
You are very unlikely to need to take any steps to exclude anonymous
ciphers, they are excluded automatically as necessary.  If you must
exclude anonymous ciphers at the "may" or "encrypt" security levels,
when the Postfix SMTP client does not need or use peer certificates, set
"smtp_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers only when
TLS is enforced, set "smtp_tls_mandatory_exclude_ciphers = aNULL". </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_tls_exclude_ciphers

<p> List of ciphers or cipher types to exclude from the Postfix
SMTP client cipher
list at all TLS security levels. This is not an OpenSSL cipherlist, it is
a simple list separated by whitespace and/or commas. The elements are a
single cipher, or one or more "+" separated cipher properties, in which
case only ciphers matching <b>all</b> the properties are excluded. </p>

<p> Examples (some of these will cause problems): </p>

<blockquote>
<pre>
smtp_tls_exclude_ciphers = aNULL
smtp_tls_exclude_ciphers = MD5, DES
smtp_tls_exclude_ciphers = DES+MD5
smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
smtp_tls_exclude_ciphers = kEDH+aRSA
</pre>
</blockquote>

<p> The first setting, disables anonymous ciphers. The next setting
disables ciphers that use the MD5 digest algorithm or the (single) DES
encryption algorithm. The next setting disables ciphers that use MD5 and
DES together.  The next setting disables the two ciphers "AES256-SHA"
and "DES-CBC3-MD5". The last setting disables ciphers that use "EDH"
key exchange with RSA authentication. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_tls_mandatory_exclude_ciphers

<p> Additional list of ciphers or cipher types to exclude from the
SMTP client cipher list at mandatory TLS security levels. This list
works in addition to the exclusions listed with smtp_tls_exclude_ciphers
(see there for syntax details).  </p>

<p> Starting with Postfix 2.6, the mandatory cipher exclusions can be
specified on a per-destination basis via the TLS policy "exclude"
attribute. See smtp_tls_policy_maps for notes and examples. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM tls_high_cipherlist ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH

<p> The OpenSSL cipherlist for "HIGH" grade ciphers. This defines
the meaning of the "high" setting in smtpd_tls_mandatory_ciphers,
smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers. You are
strongly encouraged to not change this setting. With OpenSSL 1.0.0 and
later the cipherlist may start with an "aNULL:" prefix, which restores
the 0.9.8-compatible ordering of the aNULL ciphers to the top of the
list when they are enabled. This prefix is not needed with previous
OpenSSL releases. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM tls_medium_cipherlist ALL:!EXPORT:!LOW:+RC4:@STRENGTH

<p> The OpenSSL cipherlist for "MEDIUM" or higher grade ciphers. This
defines the meaning of the "medium" setting in smtpd_tls_mandatory_ciphers,
smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers. This is
the default cipherlist for mandatory TLS encryption in the TLS
client (with anonymous ciphers disabled when verifying server
certificates). You are strongly encouraged to not change this
setting.  With OpenSSL 1.0.0 and later the cipherlist may start with an
"aNULL:" prefix, which restores the 0.9.8-compatible ordering of the
aNULL ciphers to the top of the list when they are enabled. This prefix
is not needed with previous OpenSSL releases. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM tls_low_cipherlist ALL:!EXPORT:+RC4:@STRENGTH

<p> The OpenSSL cipherlist for "LOW" or higher grade ciphers. This defines
the meaning of the "low" setting in smtpd_tls_mandatory_ciphers,
smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers. You are
strongly encouraged to not change this setting.  With OpenSSL 1.0.0 and
later the cipherlist may start with an "aNULL:" prefix, which restores
the 0.9.8-compatible ordering of the aNULL ciphers to the top of the
list when they are enabled. This prefix is not needed with previous
OpenSSL releases. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM tls_export_cipherlist ALL:+RC4:@STRENGTH

<p> The OpenSSL cipherlist for "EXPORT" or higher grade ciphers. This
defines the meaning of the "export" setting in smtpd_tls_mandatory_ciphers,
smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers. This is
the cipherlist for the opportunistic ("may") TLS client security
level and is the default cipherlist for the SMTP server. You are
strongly encouraged to not change this setting. With OpenSSL 1.0.0 and
later the cipherlist may start with an "aNULL:" prefix, which restores
the 0.9.8-compatible ordering of the aNULL ciphers to the top of the
list when they are enabled. This prefix is not needed with previous
OpenSSL releases. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM tls_null_cipherlist eNULL:!aNULL

<p> The OpenSSL cipherlist for "NULL" grade ciphers that provide
authentication without encryption. This defines the meaning of the "null"
setting in smtpd_mandatory_tls_ciphers, smtp_tls_mandatory_ciphers and
lmtp_tls_mandatory_ciphers.  You are strongly encouraged to not
change this setting. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_mandatory_ciphers

<p> The LMTP-specific version of the smtp_tls_mandatory_ciphers
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_exclude_ciphers

<p> The LMTP-specific version of the smtp_tls_exclude_ciphers
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM lmtp_tls_mandatory_exclude_ciphers

<p> The LMTP-specific version of the smtp_tls_mandatory_exclude_ciphers
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_tls_security_level

<p> The SMTP TLS security level for the Postfix SMTP server; when
a non-empty value is specified, this overrides the obsolete parameters
smtpd_use_tls and smtpd_enforce_tls. This parameter is ignored with
"smtpd_tls_wrappermode = yes".  </p>

<p> Specify one of the following security levels: </p>

<dl>

<dt><b>none</b></dt> <dd> TLS will not be used. </dd>

<dt><b>may</b></dt> <dd> Opportunistic TLS: announce STARTTLS support
to SMTP clients, but do not require that clients use TLS encryption.
</dd>

<dt><b>encrypt</b></dt> <dd>Mandatory TLS encryption: announce
STARTTLS support to SMTP clients, and require that clients use TLS
encryption. According to RFC 2487 this MUST NOT be applied in case
of a publicly-referenced SMTP server. Instead, this option should
be used only on dedicated servers. </dd>

</dl>

<p> Note 1: the "fingerprint", "verify" and "secure" levels are not
supported here.
The Postfix SMTP server logs a warning and uses "encrypt" instead.
To verify SMTP client certificates, see TLS_README for a discussion
of the smtpd_tls_ask_ccert, smtpd_tls_req_ccert, and permit_tls_clientcerts
features.  </p>

<p> Note 2: The parameter setting "smtpd_tls_security_level =
encrypt" implies "smtpd_tls_auth_only = yes".</p>

<p> Note 3: when invoked via "sendmail -bs", Postfix will never
offer STARTTLS due to insufficient privileges to access the server
private key. This is intended behavior.</p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM internal_mail_filter_classes

<p> What categories of Postfix-generated mail are subject to
before-queue content inspection by non_smtpd_milters, header_checks
and body_checks.  Specify zero or more of the following, separated
by whitespace or comma.  </p>

<dl>

<dt><b>bounce</b></dt> <dd> Inspect the content of delivery
status notifications. </dd>

<dt><b>notify</b></dt> <dd> Inspect the content of postmaster
notifications by the smtp(8) and smtpd(8) processes. </dd>

</dl>

<p> NOTE: It's generally not safe to enable content inspection of
Postfix-generated email messages. The user is warned. </p>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtpd_tls_always_issue_session_ids yes

<p> Force the Postfix SMTP server to issue a TLS session id, even
when TLS session caching is turned off (smtpd_tls_session_cache_database
is empty). This behavior is compatible with Postfix &lt; 2.3. </p>

<p> With Postfix 2.3 and later the Postfix SMTP server can disable
session id generation when TLS session caching is turned off. This
keeps clients from caching sessions that almost certainly cannot
be re-used.  </p>

<p> By default, the Postfix SMTP server always generates TLS session
ids. This works around a known defect in mail client applications
such as MS Outlook, and may also prevent interoperability issues
with other MTAs. </p>

<p> Example: </p>

<pre>
smtpd_tls_always_issue_session_ids = no
</pre>

<p> This feature is available in Postfix 2.3 and later. </p>

%PARAM smtp_pix_workarounds disable_esmtp, delay_dotcrlf

<p> A list that specifies zero or more workarounds for CISCO PIX
firewall bugs. These workarounds are implemented by the Postfix
SMTP client. Workaround names are separated by comma or space, and
are case insensitive.  This parameter setting can be overruled with
per-destination smtp_pix_workaround_maps settings. </p>

<dl>

<dt><b>delay_dotcrlf</b><dd> Insert a delay before sending
".&lt;CR&gt;&lt;LF&gt;" after the end of the message content.  The
delay is subject to the smtp_pix_workaround_delay_time and
smtp_pix_workaround_threshold_time parameter settings. </dd>

<dt><b>disable_esmtp</b><dd> Disable all extended SMTP commands:
send HELO instead of EHLO. </dd>

</dl>

<p> This feature is available in Postfix 2.4 and later. The default
settings are backwards compatible with earlier Postfix versions.
</p>

%PARAM smtp_pix_workaround_maps

<p> Lookup tables, indexed by the remote SMTP server address, with
per-destination workarounds for CISCO PIX firewall bugs.  The table
is not indexed by hostname for consistency with
smtp_discard_ehlo_keyword_address_maps. </p>

<p> This feature is available in Postfix 2.4 and later. </p>

%PARAM lmtp_pix_workarounds

<p> The LMTP-specific version of the smtp_pix_workaround
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.4 and later. </p>

%PARAM smtp_tls_fingerprint_digest md5

<p> The message digest algorithm used to construct remote SMTP server
certificate fingerprints. At the "fingerprint" TLS security level
(<b>smtp_tls_security_level</b> = fingerprint), the server certificate is
verified by directly matching its <i>fingerprint</i>. The fingerprint
is the message digest of the server certificate using the selected
algorithm. With a digest algorithm resistant to "second pre-image"
attacks, it is not feasible to create a new public key and a matching
certificate that has the same fingerprint. </p>

<p> The default algorithm is <b>md5</b>; this is consistent with
the backwards compatible setting of the digest used to verify client
certificates in the SMTP server. </p>

<p> The best practice algorithm is now <b>sha1</b>. Recent advances in hash
function cryptanalysis have led to md5 being deprecated in favor of sha1.
However, as long as there are no known "second pre-image" attacks
against md5, its use in this context can still be considered safe.
</p>

<p> While additional digest algorithms are often available with OpenSSL's
libcrypto, only those used by libssl in SSL cipher suites are available to
Postfix. For now this means just md5 or sha1. </p>

<p> To find the fingerprint of a specific certificate file, with a
specific digest algorithm, run:
</p>

<blockquote>
<pre>
$ openssl x509 -noout -fingerprint -<i>digest</i> -in <i>certfile</i>.pem
</pre>
</blockquote>

<p> The text to the right of "=" sign is the desired fingerprint.
For example: </p>

<blockquote>
<pre>
$ openssl x509 -noout -fingerprint -sha1 -in cert.pem
SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A
</pre>
</blockquote>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM smtp_tls_fingerprint_cert_match

<p> List of acceptable remote SMTP server certificate fingerprints
for the "fingerprint" TLS security level (<b>smtp_tls_security_level</b> =
fingerprint). At this security level, certificate authorities are
not used, and certificate expiration times are ignored. Instead,
server certificates are verified directly via their "fingerprint". The
fingerprint is a message digest of the server certificate. The digest
algorithm is selected via the <b>smtp_tls_fingerprint_digest</b>
parameter. </p>

<p> When an <b>smtp_tls_policy_maps</b> table entry specifies the
"fingerprint" security level, any "match" attributes in that entry specify
the list of valid fingerprints for the corresponding destination. Multiple
fingerprints can be combined with a "|" delimiter in a single match
attribute, or multiple match attributes can be employed. </p>

<p> Example: Certificate fingerprint verification with internal mailhub.
Two matching fingerprints are listed. The relayhost may be multiple
physical hosts behind a load-balancer, each with its own private/public
key and self-signed certificate. Alternatively, a single relayhost may
be in the process of switching from one set of private/public keys to
another, and both keys are trusted just prior to the transition. </p>

<blockquote>
<pre>
relayhost = [mailhub.example.com]
smtp_tls_security_level = fingerprint
smtp_tls_fingerprint_digest = md5
smtp_tls_fingerprint_cert_match =
    3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
    EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
</pre>
</blockquote>

<p> Example: Certificate fingerprint verification with selected destinations.
As in the example above, we show two matching fingerprints: </p>

<blockquote>
<pre>
/etc/postfix/main.cf:
    smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
    smtp_tls_fingerprint_digest = md5
</pre>
</blockquote>

<blockquote>
<pre>
/etc/postfix/tls_policy:
    example.com	fingerprint
        match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
        match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
</pre>
</blockquote>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM lmtp_tls_fingerprint_cert_match

<p> The LMTP-specific version of the smtp_tls_fingerprint_cert_match
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM lmtp_tls_fingerprint_digest md5

<p> The LMTP-specific version of the smtp_tls_fingerprint_digest
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM smtpd_tls_fingerprint_digest md5

<p> The message digest algorithm used to construct client-certificate
fingerprints for <b>check_ccert_access</b> and
<b>permit_tls_clientcerts</b>. The default algorithm is <b>md5</b>,
for backwards compatibility with Postfix releases prior to 2.5.
</p>

<p> The best practice algorithm is now <b>sha1</b>. Recent advances in hash
function cryptanalysis have led to md5 being deprecated in favor of sha1.
However, as long as there are no known "second pre-image" attacks
against md5, its use in this context can still be considered safe.
</p>

<p> While additional digest algorithms are often available with OpenSSL's
libcrypto, only those used by libssl in SSL cipher suites are available to
Postfix. For now this means just md5 or sha1. </p>

<p> To find the fingerprint of a specific certificate file, with a
specific digest algorithm, run: </p>

<blockquote>
<pre>
$ openssl x509 -noout -fingerprint -<i>digest</i> -in <i>certfile</i>.pem
</pre>
</blockquote>

<p> The text to the right of "=" sign is the desired fingerprint.
For example: </p>

<blockquote>
<pre>
$ openssl x509 -noout -fingerprint -sha1 -in cert.pem
SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A
</pre>
</blockquote>

<p> Example: client-certificate access table, with sha1 fingerprints: </p>

<blockquote>
<pre>
/etc/postfix/main.cf:
    smtpd_tls_fingerprint_digest = sha1
    smtpd_client_restrictions =
        check_ccert_access hash:/etc/postfix/access,
        reject
</pre>
<pre>
/etc/postfix/access:
    # Action folded to next line...
    AF:88:7C:AD:51:95:6F:36:96:F6:01:FB:2E:48:CD:AB:49:25:A2:3B
        OK
    85:16:78:FD:73:6E:CE:70:E0:31:5F:0D:3C:C8:6D:C4:2C:24:59:E1
        permit_auth_destination
</pre>
</blockquote>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM lmtp_pix_workaround_maps

<p> The LMTP-specific version of the smtp_pix_workaround_maps
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.4 and later. </p>

%PARAM detect_8bit_encoding_header yes

<p> Automatically detect 8BITMIME body content by looking at
Content-Transfer-Encoding: message headers; historically, this
behavior was hard-coded to be "always on".  </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM send_cyrus_sasl_authzid no

<p> When authenticating to a remote SMTP or LMTP server with the
default setting "no", send no SASL authoriZation ID (authzid); send
only the SASL authentiCation ID (authcid) plus the authcid's password.
</p>

<p> The non-default setting "yes" enables the behavior of older
Postfix versions.  These always send a SASL authzid that is equal
to the SASL authcid, but this causes inter-operability problems
with some SMTP servers. </p>

<p> This feature is available in Postfix 2.4.4 and later. </p>

%PARAM smtpd_client_port_logging no

<p> Enable logging of the remote SMTP client port in addition to
the hostname and IP address. The logging format is "host[address]:port".
</p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM qmqpd_client_port_logging no

<p> Enable logging of the remote QMQP client port in addition to
the hostname and IP address. The logging format is "host[address]:port".
</p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM smtp_tls_protocols !SSLv2

<p> List of TLS protocols that the Postfix SMTP client will exclude or
include with opportunistic TLS encryption. Starting with Postfix 2.6,
the Postfix SMTP client will by default not use the obsolete SSLv2
protocol. </p>

<p> In main.cf the values are separated by whitespace, commas or
colons. In the policy table (see smtp_tls_policy_maps) the only valid
separator is colon. An empty value means allow all protocols. The valid
protocol names, (see <b>SSL_get_version(3)</b>), are "SSLv2", "SSLv3"
and "TLSv1". </p>

<p> To include a protocol list its name, to exclude it, prefix the name
with a "!" character. To exclude SSLv2 even for opportunistic TLS set
"smtp_tls_protocols = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
"smtp_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the protocols to
include, is supported, but not recommended. OpenSSL provides no mechanisms
for excluding protocols not known at compile-time. If Postfix is linked
against an OpenSSL library that supports additional protocol versions,
they cannot be excluded using either syntax. </p>

<p> Example: </p>
<pre>
# TLSv1 only!
smtp_tls_protocols = !SSLv2, !SSLv3
</pre>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM smtpd_tls_protocols

<p> List of TLS protocols that the Postfix SMTP server will exclude
or include with opportunistic TLS encryption. This parameter SHOULD be
left at its default empty value, allowing all protocols to be used with
opportunistic TLS. </p>

<p> In main.cf the values are separated by whitespace, commas or
colons. An empty value means allow all protocols. The valid protocol
names, (see <b>SSL_get_version(3)</b>), are "SSLv2", "SSLv3" and
"TLSv1". In smtp_tls_policy_maps table entries, "protocols" attribute
values are separated by a colon. </p>

<p> To include a protocol list its name, to exclude it, prefix the name
with a "!" character. To exclude SSLv2 even for opportunistic TLS set
"smtpd_tls_protocols = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
"smtpd_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the protocols to
include, is supported, but not recommended. OpenSSL provides no mechanisms
for excluding protocols not known at compile-time. If Postfix is linked
against an OpenSSL library that supports additional protocol versions,
they cannot be excluded using either syntax. </p>

<p> Example: </p>
<pre>
smtpd_tls_protocols = !SSLv2
</pre>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM lmtp_tls_protocols

<p> The LMTP-specific version of the smtp_tls_protocols configuration
parameter. See there for details. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM smtp_tls_ciphers export

<p> The minimum TLS cipher grade that the Postfix SMTP client
will use with opportunistic TLS encryption. Cipher types listed in
smtp_tls_exclude_ciphers are excluded from the base definition of
the selected cipher grade. The default value "export" ensures maximum
inter-operability. Because encryption is optional, stronger controls
are not appropriate, and this setting SHOULD NOT be changed unless the
change is essential. </p>

<p> When TLS is mandatory the cipher grade is chosen via the
smtp_tls_mandatory_ciphers configuration parameter, see there for syntax
details. See smtp_tls_policy_maps for information on how to configure
ciphers on a per-destination basis. </p>

<p> Example: </p>
<pre>
smtp_tls_ciphers = export
</pre>

<p> This feature is available in Postfix 2.6 and later. With earlier Postfix
releases only the smtp_tls_mandatory_ciphers parameter is implemented,
and opportunistic TLS always uses "export" or better (i.e. all) ciphers. </p>

%PARAM smtpd_tls_ciphers export

<p> The minimum TLS cipher grade that the Postfix SMTP server
will use with opportunistic TLS encryption. Cipher types listed in
smtpd_tls_exclude_ciphers are excluded from the base definition of
the selected cipher grade. The default value "export" ensures maximum
inter-operability. Because encryption is optional, stronger controls
are not appropriate, and this setting SHOULD NOT be changed unless the
change is essential. </p>

<p> When TLS is mandatory the cipher grade is chosen via the
smtpd_tls_mandatory_ciphers configuration parameter, see there for syntax
details. </p>

<p> Example: </p>
<pre>
smtpd_tls_ciphers = export
</pre>

<p> This feature is available in Postfix 2.6 and later. With earlier Postfix
releases only the smtpd_tls_mandatory_ciphers parameter is implemented,
and opportunistic TLS always uses "export" or better (i.e. all) ciphers. </p>

%PARAM lmtp_tls_ciphers export

<p> The LMTP-specific version of the smtp_tls_ciphers configuration
parameter. See there for details. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM tls_eecdh_strong_curve prime256v1

<p> The elliptic curve used by the SMTP server for sensibly strong
ephemeral ECDH key exchange. This curve is used by the Postfix SMTP
server when "smtpd_tls_eecdh_grade = strong". The phrase "sensibly
strong" means approximately 128-bit security based on best known
attacks. The selected curve must be implemented by OpenSSL (as
reported by ecparam(1) with the "-list_curves" option) and be one
of the curves listed in Section 5.1.1 of RFC 4492. You should not
generally change this setting. </p>

<p> This default curve is specified in NSA "Suite B" Cryptography
(see http://www.nsa.gov/ia/industry/crypto_suite_b.cfm) for
information classified as SECRET. </p>

<p> Note: elliptic curve names are poorly standardized; different
standards groups are assigning different names to the same underlying
curves.  The curve with the X9.62 name "prime256v1" is also known
under the SECG name "secp256r1", but OpenSSL does not recognize the
latter name. </p>

<p> This feature is available in Postfix 2.6 and later, when it is
compiled and linked with OpenSSL 1.0.0 or later. </p>

%PARAM tls_eecdh_ultra_curve secp384r1

<p> The elliptic curve used by the SMTP server for maximally strong
ephemeral ECDH key exchange. This curve is used by the Postfix SMTP
server when "smtpd_tls_eecdh_grade = ultra". The phrase "maximally
strong" means approximately 192-bit security based on best known attacks.
This additional strength comes at a significant computational cost, most
users should instead set "smtpd_tls_eecdh_grade = strong".  The selected
curve must be implemented by OpenSSL (as reported by ecparam(1) with the
"-list_curves" option) and be one of the curves listed in Section 5.1.1
of RFC 4492. You should not generally change this setting. </p>

<p> This default "ultra" curve is specified in NSA "Suite B" Cryptography
(see http://www.nsa.gov/ia/industry/crypto_suite_b.cfm) for information
classified as TOP SECRET. </p>

<p> This feature is available in Postfix 2.6 and later, when it is
compiled and linked with OpenSSL 1.0.0 or later. </p>

%PARAM smtpd_tls_eecdh_grade see "postconf -d" output

<p> The Postfix SMTP server security grade for ephemeral elliptic-curve
Diffie-Hellman (EECDH) key exchange. </p>

<p> The available choices are: </p>

<dl>

<dt><b>none</b></dt> <dd> Don't use EECDH. Ciphers based on EECDH key
exchange will be disabled. This is the default in official Postfix
releases (mail_version = major.minor.patchlevel). </dd>

<dt><b>strong</b></dt> <dd> Use EECDH with approximately 128
bits of security at a reasonable computational cost. This is the
current best-practice trade-off between security and computational
efficiency. This is the default in Postfix snapshot releases
(mail_version = major.minor-releasedate). </dd>

<dt><b>ultra</b></dt> <dd> Use EECDH with approximately 192 bits of
security at computational cost that is approximately twice as high
as 128 bit strength ECC. Barring significant progress in attacks on
elliptic curve crypto-systems, the "strong" curve is sufficient for most
users. </dd>

</dl>

<p> This feature is available in Postfix 2.6 and later, when it is
compiled and linked with OpenSSL 1.0.0 or later. </p>

%PARAM smtpd_tls_eccert_file

<p> File with the Postfix SMTP server ECDSA certificate in PEM format.
This file may also contain the Postfix SMTP server private ECDSA key. </p>

<p> See the discussion under smtpd_tls_cert_file for more details. </p>

<p> Example: </p>

<pre>
smtpd_tls_eccert_file = /etc/postfix/ecdsa-scert.pem
</pre>

<p> This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later. </p>

%PARAM smtpd_tls_eckey_file $smtpd_tls_eccert_file

<p> File with the Postfix SMTP server ECDSA private key in PEM format.
This file may be combined with the Postfix SMTP server ECDSA certificate
file specified with $smtpd_tls_eccert_file. </p>

<p> The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account ("root"), and no access
to anyone else. </p>

<p> This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later. </p>

%PARAM smtp_tls_eccert_file

<p> File with the Postfix SMTP client ECDSA certificate in PEM format.
This file may also contain the Postfix SMTP client ECDSA private key. </p>

<p> See the discussion under smtp_tls_cert_file for more details.
</p>

<p> Example: </p>

<pre>
smtp_tls_eccert_file = /etc/postfix/ecdsa-ccert.pem
</pre>

<p> This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later. </p>

%PARAM smtp_tls_eckey_file $smtp_tls_eccert_file

<p> File with the Postfix SMTP client ECDSA private key in PEM format.
This file may be combined with the Postfix SMTP client ECDSA
certificate file specified with $smtp_tls_eccert_file. </p>

<p> The private key must be accessible without a pass-phrase, i.e. it
must not be encrypted. File permissions should grant read-only
access to the system superuser account ("root"), and no access
to anyone else. </p>

<p> This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later. </p>

%PARAM lmtp_tls_eccert_file

<p> The LMTP-specific version of the smtp_tls_eccert_file configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later. </p>

%PARAM lmtp_tls_eckey_file

<p> The LMTP-specific version of the smtp_tls_eckey_file configuration
parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later. </p>

%PARAM smtp_header_checks

<p> Restricted header_checks(5) tables for the Postfix SMTP client.
These tables are searched while mail is being delivered.  Actions
that change the delivery time or destination are not available.
</p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM smtp_mime_header_checks

<p> Restricted mime_header_checks(5) tables for the Postfix SMTP
client. These tables are searched while mail is being delivered.
Actions that change the delivery time or destination are not
available.  </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM smtp_nested_header_checks

<p> Restricted nested_header_checks(5) tables for the Postfix SMTP
client. These tables are searched while mail is being delivered.
Actions that change the delivery time or destination are not
available.  </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM smtp_body_checks

<p> Restricted body_checks(5) tables for the Postfix SMTP client.
These tables are searched while mail is being delivered.  Actions
that change the delivery time or destination are not available.
</p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM destination_concurrency_feedback_debug no

<p> Make the queue manager's feedback algorithm verbose for performance
analysis purposes. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM default_destination_concurrency_failed_cohort_limit 1

<p> How many pseudo-cohorts must suffer connection or handshake
failure before a specific destination is considered unavailable
(and further delivery is suspended). Specify zero to disable this
feature. A destination's pseudo-cohort failure count is reset each
time a delivery completes without connection or handshake failure
for that specific destination. </p>

<p> A pseudo-cohort is the number of deliveries equal to a destination's
delivery concurrency. </p>

<p> Use <i>transport</i>_destination_concurrency_failed_cohort_limit to specify
a transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport. </p>

<p> This feature is available in Postfix 2.5. The default setting
is compatible with earlier Postfix versions. </p>

%PARAM default_destination_concurrency_negative_feedback 1

<p> The per-destination amount of delivery concurrency negative
feedback, after a delivery completes with a connection or handshake
failure. Feedback values are in the range 0..1 inclusive. With
negative feedback, concurrency is decremented at the beginning of
a sequence of length 1/feedback. This is unlike positive feedback,
where concurrency is incremented at the end of a sequence of length
1/feedback. </p>

<p> As of Postfix version 2.5, negative feedback cannot reduce
delivery concurrency to zero.  Instead, a destination is marked
dead (further delivery suspended) after the failed pseudo-cohort
count reaches $default_destination_concurrency_failed_cohort_limit
(or $<i>transport</i>_destination_concurrency_failed_cohort_limit).
To make the scheduler completely immune to connection or handshake
failures, specify a zero feedback value and a zero failed pseudo-cohort
limit.  </p>

<p> Specify one of the following forms: </p>

<dl>

<dt> <b><i>number</i> </b> </dt>

<dt> <b><i>number</i> / <i>number</i> </b> </dt>

<dd> Constant feedback. The value must be in the range 0..1 inclusive.
The default setting of "1" is compatible with Postfix versions
before 2.5, where a destination's delivery concurrency is throttled
down to zero (and further delivery suspended) after a single failed
pseudo-cohort. </dd>

<dt> <b><i>number</i> / concurrency </b> </dt>

<dd> Variable feedback of "<i>number</i> / (delivery concurrency)".
The <i>number</i> must be in the range 0..1 inclusive. With
<i>number</i> equal to "1", a destination's delivery concurrency
is decremented by 1 after each failed pseudo-cohort.  </dd>

<!--

<dt> <b><i>number</i> / sqrt_concurrency </b> </dt>

<dd> Variable feedback of "<i>number</i> / sqrt(delivery concurrency)".
The <i>number</i> must be in the range 0..1 inclusive. This setting
may be removed in a future version.  </dd>

-->

</dl>

<p> A pseudo-cohort is the number of deliveries equal to a destination's
delivery concurrency. </p>

<p> Use <i>transport</i>_destination_concurrency_negative_feedback
to specify a transport-specific override, where <i>transport</i>
is the master.cf
name of the message delivery transport. </p>

<p> This feature is available in Postfix 2.5. The default setting
is compatible with earlier Postfix versions. </p>

%PARAM default_destination_concurrency_positive_feedback 1

<p> The per-destination amount of delivery concurrency positive
feedback, after a delivery completes without connection or handshake
failure. Feedback values are in the range 0..1 inclusive.  The
concurrency increases until it reaches the per-destination maximal
concurrency limit. With positive feedback, concurrency is incremented
at the end of a sequence with length 1/feedback. This is unlike
negative feedback, where concurrency is decremented at the start
of a sequence of length 1/feedback. </p>

<p> Specify one of the following forms:  </p>

<dl>

<dt> <b><i>number</i> </b> </dt>

<dt> <b><i>number</i> / <i>number</i> </b> </dt>

<dd> Constant feedback.  The value must be in the range 0..1
inclusive. The default setting of "1" is compatible with Postfix
versions before 2.5, where a destination's delivery concurrency
doubles after each successful pseudo-cohort.  </dd>

<dt> <b><i>number</i> / concurrency </b> </dt>

<dd> Variable feedback of "<i>number</i> / (delivery concurrency)".
The <i>number</i> must be in the range 0..1 inclusive. With
<i>number</i> equal to "1", a destination's delivery concurrency
is incremented by 1 after each successful pseudo-cohort.  </dd>

<!--

<dt> <b><i>number</i> / sqrt_concurrency </b> </dt>

<dd> Variable feedback of "<i>number</i> / sqrt(delivery concurrency)".
The <i>number</i> must be in the range 0..1 inclusive. This setting
may be removed in a future version.  </dd>

-->

</dl>

<p> A pseudo-cohort is the number of deliveries equal to a destination's
delivery concurrency. </p>

<p> Use <i>transport</i>_destination_concurrency_positive_feedback
to specify a transport-specific override, where <i>transport</i>
is the master.cf name of the message delivery transport. </p>

<p> This feature is available in Postfix 2.5 and later.  </p>

%PARAM transport_destination_concurrency_failed_cohort_limit $default_destination_concurrency_failed_cohort_limit

<p> A transport-specific override for the
default_destination_concurrency_failed_cohort_limit parameter value,
where <i>transport</i> is the master.cf name of the message delivery
transport. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM transport_destination_concurrency_positive_feedback $default_destination_concurrency_positive_feedback

<p> A transport-specific override for the
default_destination_concurrency_positive_feedback parameter value,
where <i>transport</i> is the master.cf name of the message delivery
transport. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM transport_destination_concurrency_negative_feedback $default_destination_concurrency_negative_feedback

<p> A transport-specific override for the
default_destination_concurrency_negative_feedback parameter value,
where <i>transport</i> is the master.cf name of the message delivery
transport. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM transport_initial_destination_concurrency $initial_destination_concurrency

<p> A transport-specific override for the initial_destination_concurrency
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM transport_destination_concurrency_limit $default_destination_concurrency_limit

<p> A transport-specific override for the
default_destination_concurrency_limit parameter value, where
<i>transport</i> is the master.cf name of the message delivery
transport. </p>

%PARAM transport_destination_recipient_limit $default_destination_recipient_limit

<p> A transport-specific override for the
default_destination_recipient_limit parameter value, where
<i>transport</i> is the master.cf name of the message delivery
transport. </p>

%PARAM transport_time_limit $command_time_limit

<p> A transport-specific override for the command_time_limit parameter
value, where <i>transport</i> is the master.cf name of the message
delivery transport. </p>

%PARAM transport_delivery_slot_cost $default_delivery_slot_cost

<p> A transport-specific override for the default_delivery_slot_cost
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

%PARAM transport_delivery_slot_loan $default_delivery_slot_loan

<p> A transport-specific override for the default_delivery_slot_loan
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

%PARAM transport_delivery_slot_discount $default_delivery_slot_discount

<p> A transport-specific override for the default_delivery_slot_discount
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

%PARAM transport_minimum_delivery_slots $default_minimum_delivery_slots

<p> A transport-specific override for the default_minimum_delivery_slots
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

%PARAM transport_recipient_limit $default_recipient_limit

<p> A transport-specific override for the default_recipient_limit
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

%PARAM transport_extra_recipient_limit $default_extra_recipient_limit

<p> A transport-specific override for the default_extra_recipient_limit
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

%PARAM transport_recipient_refill_limit $default_recipient_refill_limit

<p> A transport-specific override for the default_recipient_refill_limit
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

<p> This feature is available in Postfix 2.4 and later. </p>

%PARAM transport_recipient_refill_delay $default_recipient_refill_delay

<p> A transport-specific override for the default_recipient_refill_delay
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

<p> This feature is available in Postfix 2.4 and later. </p>

%PARAM default_destination_rate_delay 0s

<p> The default amount of delay that is inserted between individual
deliveries to the same destination; with per-destination recipient
limit &gt; 1, a destination is a domain, otherwise it is a recipient.
</p>

<p> To enable the delay, specify a non-zero time value (an integral
value plus an optional one-letter suffix that specifies the time
unit). </p>

<p> Time units: s (seconds), m (minutes), h (hours), d (days), w
(weeks). The default time unit is s (seconds). </p>

<p> NOTE: the delay is enforced by the queue manager. The delay
timer state does not survive "<b>postfix reload</b>" or "<b>postfix
stop</b>".
</p>

<p> Use <i>transport</i>_destination_rate_delay to specify a
transport-specific override, where <i>transport</i> is the master.cf
name of the message delivery transport.
</p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM transport_destination_rate_delay $default_destination_rate_delay

<p> A transport-specific override for the default_destination_rate_delay
parameter value, where <i>transport</i> is the master.cf name of
the message delivery transport. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM data_directory see "postconf -d" output

<p> The directory with Postfix-writable data files (for example:
caches, pseudo-random numbers).  This directory must be owned by
the mail_owner account, and must not be shared with non-Postfix
software.  </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM stress

<p> This feature is documented in the STRESS_README document. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM smtp_sasl_auth_soft_bounce yes

<p> When a remote SMTP server rejects a SASL authentication request
with a 535 reply code, defer mail delivery instead of returning
mail as undeliverable. The latter behavior was hard-coded prior to
Postfix version 2.5. </p>

<p> Note: the setting "yes" overrides the global soft_bounce
parameter, but the setting "no" does not. </p>

<p> Example: </p>

<pre>
# Default as of Postfix 2.5
smtp_sasl_auth_soft_bounce = yes
# The old hard-coded default
smtp_sasl_auth_soft_bounce = no
</pre>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM smtp_sasl_auth_cache_name

<p> An optional table to prevent repeated SASL authentication
failures with the same remote SMTP server hostname, username and
password. Each table (key, value) pair contains a server name, a
username and password, and the full server response. This information
is stored when a remote SMTP server rejects an authentication attempt
with a 535 reply code.  As long as the smtp_sasl_password_maps
information does no change, and as long as the smtp_sasl_auth_cache_name
information does not expire (see smtp_sasl_auth_cache_time) the
Postfix SMTP client avoids SASL authentication attempts with the
same server, username and password, and instead bounces or defers
mail as controlled with the smtp_sasl_auth_soft_bounce configuration
parameter.  </p>

<p> Use a per-destination delivery concurrency of 1 (for example,
"smtp_destination_concurrency_limit = 1",
"relay_destination_concurrency_limit = 1", etc.), otherwise multiple
delivery agents may experience a login failure at the same time.
</p>

<p> The table must be accessed via the proxywrite service, i.e. the
map name must start with "proxy:". The table should be stored under
the directory specified with the data_directory parameter. </p>

<p> This feature uses cryptographic hashing to protect plain-text
passwords, and requires that Postfix is compiled with TLS support.
</p>

<p> Example: </p>

<pre>
smtp_sasl_auth_cache_name = proxy:btree:/var/db/postfix/sasl_auth_cache
</pre>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM smtp_sasl_auth_cache_time 90d

<p> The maximal age of an smtp_sasl_auth_cache_name entry before it
is removed. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM lmtp_sasl_auth_soft_bounce yes

<p> The LMTP-specific version of the smtp_sasl_auth_soft_bounce
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM lmtp_sasl_auth_cache_name

<p> The LMTP-specific version of the smtp_sasl_auth_cache_name
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM lmtp_sasl_auth_cache_time 90d

<p> The LMTP-specific version of the smtp_sasl_auth_cache_time
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM unverified_sender_reject_reason

<p> The Postfix SMTP server's reply when rejecting mail with
reject_unverified_sender. Do not include the numeric SMTP reply
code or the enhanced status code. By default, the response includes
actual address verification details.

<p> Example: </p>

<pre>
unverified_sender_reject_reason = Sender address lookup failed
</pre>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM unverified_recipient_reject_reason

<p> The Postfix SMTP server's reply when rejecting mail with
reject_unverified_recipient. Do not include the numeric SMTP reply
code or the enhanced status code. By default, the response includes
actual address verification details.

<p> Example: </p>

<pre>
unverified_recipient_reject_reason = Recipient address lookup failed
</pre>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM strict_mailbox_ownership yes

<p> Defer delivery when a mailbox file is not owned by its recipient.
The default setting is not backwards compatible.  </p>

<p> This feature is available in Postfix 2.5.3 and later. </p>

%PARAM proxymap_service_name proxymap

<p> The name of the proxymap read-only table lookup service.  This
service is normally implemented by the proxymap(8) daemon. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM proxywrite_service_name proxywrite

<p> The name of the proxywrite read-write table lookup service.
This service is normally implemented by the proxymap(8) daemon.
</p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM master_service_disable

<p> Selectively disable master(8) listener ports by service type
or by service name and type.  Specify a list of service types
("inet", "unix", "fifo", or "pass") or "name.type" tuples, where
"name" is the first field of a master.cf entry and "type" is a
service type. As with other Postfix matchlists, a search stops at
the first match.  Specify "!pattern" to exclude a service from the
list. By default, all master(8) listener ports are enabled.  </p>

<p> Note: this feature does not support "/file/name" or "type:table"
patterns, nor does it support wildcards such as "*" or "all". This
is intentional. </p>

<p> Examples: </p>

<pre>
# Turn on all master(8) listener ports (the default).
master_service_disable =
# Turn off only the main SMTP listener port.
master_service_disable = smtp.inet
# Turn off all TCP/IP listener ports.
master_service_disable = inet
# Turn off all TCP/IP listener ports except "foo".
master_service_disable = !foo.inet, inet
</pre>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM tcp_windowsize 0

<p> An optional workaround for routers that break TCP window scaling.
Specify a value &gt; 0 and &lt; 65536 to enable this feature.  With
Postfix TCP servers (smtpd(8), qmqpd(8)), this feature is implemented
by the Postfix master(8) daemon.  </p>

<p> To change this parameter without stopping Postfix, you need to
first terminate all Postfix TCP servers: </p>

<blockquote>
<pre>
# postconf -e master_service_disable=inet
# postfix reload
</pre>
</blockquote>

<p> This immediately terminates all processes that accept network
connections.  Next, you enable Postfix TCP servers with the updated
tcp_windowsize setting: </p>

<blockquote>
<pre>
# postconf -e tcp_windowsize=65535 master_service_disable=
# postfix reload
</pre>
</blockquote>

<p> If you skip these steps with a running Postfix system, then the
tcp_windowsize change will work only for Postfix TCP clients (smtp(8),
lmtp(8)).  </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM multi_instance_directories

<p> An optional list of non-default Postfix configuration directories;
these directories belong to additional Postfix instances that share
the Postfix executable files and documentation with the default
Postfix instance, and that are started, stopped, etc., together
with the default Postfix instance.  Specify a list of pathnames
separated by comma or whitespace.  </p>

<p> When $multi_instance_directories is empty, the postfix(1) command
runs in single-instance mode and operates on a single Postfix
instance only. Otherwise, the postfix(1) command runs in multi-instance
mode and invokes the multi-instance manager specified with the
multi_instance_wrapper parameter. The multi-instance manager in
turn executes postfix(1) commands for the default instance and for
all Postfix instances in $multi_instance_directories.  </p>

<p> Currently, this parameter setting is ignored except for the
default main.cf file. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM multi_instance_wrapper

<p> The pathname of a multi-instance manager command that the
postfix(1) command invokes when the multi_instance_directories
parameter value is non-empty. The pathname may be followed by
initial command arguments separated by whitespace; shell
metacharacters such as quotes are not supported in this context.
</p>

<p> The postfix(1) command invokes the manager command with the
postfix(1) non-option command arguments on the manager command line,
and with all installation configuration parameters exported into
the manager command process environment. The manager command in
turn invokes the postfix(1) command for individual Postfix instances
as "postfix -c <i>config_directory</i> <i>command</i>".  </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM multi_instance_group

<p> The optional instance group name of this Postfix instance. A
group identifies closely-related Postfix instances that the
multi-instance manager can start, stop, etc., as a unit.  This
parameter is reserved for the multi-instance manager. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM multi_instance_name

<p> The optional instance name of this Postfix instance. This name
becomes also the default value for the syslog_name parameter. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM multi_instance_enable no

<p> Allow this Postfix instance to be started, stopped, etc., by a
multi-instance manager.  By default, new instances are created in
a safe state that prevents them from being started inadvertently.
This parameter is reserved for the multi-instance manager.  </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM reject_tempfail_action defer_if_permit

<p> The Postfix SMTP server's action when a reject-type restriction
fails due to a temporary error condition. Specify "defer" to defer
the remote SMTP client request immediately. With the default
"defer_if_permit" action, the Postfix SMTP server continues to look
for opportunities to reject mail, and defers the client request
only if it would otherwise be accepted. </p>

<p> For finer control, see: unverified_recipient_tempfail_action,
unverified_sender_tempfail_action, unknown_address_tempfail_action,
and unknown_helo_hostname_tempfail_action.  </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM unverified_recipient_tempfail_action $reject_tempfail_action

<p> The Postfix SMTP server's action when reject_unverified_recipient
fails due to a temporary error condition. Specify "defer" to defer
the remote SMTP client request immediately. With the default
"defer_if_permit" action, the Postfix SMTP server continues to look
for opportunities to reject mail, and defers the client request
only if it would otherwise be accepted. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM unverified_sender_tempfail_action $reject_tempfail_action

<p> The Postfix SMTP server's action when reject_unverified_sender
fails due to a temporary error condition. Specify "defer" to defer
the remote SMTP client request immediately. With the default
"defer_if_permit" action, the Postfix SMTP server continues to look
for opportunities to reject mail, and defers the client request
only if it would otherwise be accepted. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM unknown_address_tempfail_action $reject_tempfail_action

<p> The Postfix SMTP server's action when reject_unknown_sender_domain
or reject_unknown_recipient_domain fail due to a temporary error
condition. Specify "defer" to defer the remote SMTP client request
immediately. With the default "defer_if_permit" action, the Postfix
SMTP server continues to look for opportunities to reject mail, and
defers the client request only if it would otherwise be accepted.
</p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM unknown_helo_hostname_tempfail_action $reject_tempfail_action

<p> The Postfix SMTP server's action when reject_unknown_helo_hostname
fails due to an temporary error condition. Specify "defer" to defer
the remote SMTP client request immediately. With the default
"defer_if_permit" action, the Postfix SMTP server continues to look
for opportunities to reject mail, and defers the client request
only if it would otherwise be accepted. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM postmulti_start_commands start

<p> The postfix(1) commands that the postmulti(1) instance manager treats
as "start" commands. For these commands, disabled instances are "checked"
rather than "started", and failure to "start" a member instance of an
instance group will abort the start-up of later instances. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM postmulti_stop_commands see "postconf -d" output

<p> The postfix(1) commands that the postmulti(1) instance manager treats
as "stop" commands. For these commands, disabled instances are skipped,
and enabled instances are processed in reverse order. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM postmulti_control_commands reload flush

<p> The postfix(1) commands that the postmulti(1) instance manager
treats as "control" commands, that operate on running instances. For
these commands, disabled instances are skipped. </p>

<p> This feature is available in Postfix 2.6 and later. </p>

%PARAM lmtp_assume_final no

<p> When an LMTP server announces no DSN support, assume that the
server performs final delivery, and send "delivered" delivery status
notifications instead of "relayed". The default setting is backwards
compatible to avoid the infinetisimal possibility of breaking
existing LMTP-based content filters. </p>

%PARAM always_add_missing_headers no

<p> Always add (Resent-) From:, To:, Date: or Message-ID: headers
when not present.  Postfix 2.6 and later add these headers only
when clients match the local_header_rewrite_clients parameter
setting.  Earlier Postfix versions always add these headers; this
may break DKIM signatures that cover non-existent headers. </p>

%PARAM lmtp_header_checks

<p> The LMTP-specific version of the smtp_header_checks configuration
parameter. See there for details. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM lmtp_mime_header_checks

<p> The LMTP-specific version of the smtp_mime_header_checks
configuration parameter. See there for details. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM lmtp_nested_header_checks

<p> The LMTP-specific version of the smtp_nested_header_checks
configuration parameter. See there for details. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM lmtp_body_checks

<p> The LMTP-specific version of the smtp_body_checks configuration
parameter. See there for details. </p>

<p> This feature is available in Postfix 2.5 and later. </p>

%PARAM milter_header_checks

<p> Optional lookup tables for content inspection of message headers
that are produced by Milter applications.  See the header_checks(5)
manual page available actions. Currently, PREPEND is not implemented.
</p>

<p> The following example sends all mail that is marked as SPAM to
a spam handling machine. Note that matches are case-insensitive
by default. </p>

<pre>
/etc/postfix/main.cf:
    milter_header_checks = pcre:/etc/postfix/milter_header_checks
</pre>

<pre>
/etc/postfix/milter_header_checks:
    /^X-SPAM-FLAG:\s+YES/ FILTER mysmtp:sanitizer.example.com:25
</pre>

<p> The milter_header_checks mechanism could also be used for
whitelisting. For example it could be used to skip heavy content
inspection for DKIM-signed mail from known friendly domains. </p>

<p> This feature is available in Postfix 2.7, and as an optional
patch for Postfix 2.6. </p>

%PARAM smtpd_command_filter

<p> A mechanism to transform commands from remote SMTP clients.
This is a last-resort tool to work around client commands that break
inter-operability with the Postfix SMTP server.  Other uses involve
fault injection to test Postfix's handling of invalid commands.
</p>

<p> Specify the name of a "type:table" lookup table. The search
string is the SMTP command as received from the remote SMTP client,
except that initial whitespace and the trailing &lt;CR&gt;&lt;LF&gt;
are removed.  The result value is executed by the Postfix SMTP
server.  </p>

<p> Postfix already implements a number of workarounds for malformed
client commands. </p>

<ul>

<li> <p> Use "resolve_numeric_domain = yes" to accept
"<i>user@ipaddress</i>". </p>

<li> <p> Postfix already accepts the correct form
"<i>user@[ipaddress]</i>".  </p>

<li> <p> Use "strict_rfc821_envelopes = no" to accept "<i>User Name
&lt;user@example.com&gt;</i>". Postfix will ignore the "User Name"
part before delivering the mail. </p>

</ul>

<p> Examples: </p>

<pre>
/etc/postfix/main.cf:
    smtpd_command_filter = pcre:/etc/postfix/command_filter
</pre>

<pre>
/etc/postfix/command_filter:
    # Work around clients that send malformed HELO commands.
    /^HELO\s*$/ HELO domain.invalid
</pre>

<pre>
    # Work around clients that send empty lines.
    /^\s*$/     NOOP
</pre>

<pre>
    # Work around clients that send RCPT TO:&lt;'user@domain'&gt;.
    # WARNING: do not lose the parameters that follow the address.
    /^RCPT\s+TO:\s*&lt;'([^[:space:]]+)'&gt;(.*)/     RCPT TO:&lt;$1&gt;$2
</pre>

<p> This feature is available in Postfix 2.7. </p>

%PARAM smtp_reply_filter

<p> A mechanism to transform replies from remote SMTP servers one
line at a time.  This is a last-resort tool to work around server
replies that break inter-operability with the Postfix SMTP client.
Other uses involve fault injection to test Postfix's handling of
invalid responses. </p>

<p> Notes: </p>

<ul>

<li> <p> In the case of a multi-line reply, the Postfix SMTP client
uses the final reply line's numerical SMTP reply code and enhanced
status code.  </p>

<li> <p> The numerical SMTP reply code (XYZ) takes precedence over
the enhanced status code (X.Y.Z).  When the enhanced status code
initial digit differs from the SMTP reply code initial digit, or
when no enhanced status code is present, the Postfix SMTP client
uses a generic enhanced status code (X.0.0) instead. </p>

</ul>

<p> Specify the name of a "type:table" lookup table. The search
string is a single SMTP reply line as received from the remote SMTP
server, except that the trailing &lt;CR&gt;&lt;LF&gt; are removed.  </p>

<p> Examples: </p>

<pre>
/etc/postfix/main.cf:
    smtp_reply_filter = pcre:/etc/postfix/reply_filter
</pre>

<pre>
/etc/postfix/reply_filter:
    # Transform garbage into "250-filler..." so that it looks like
    # one line from a multi-line reply. It does not matter what we
    # substitute here as long it has the right syntax.  The Postfix
    # SMTP client will use the final line's numerical SMTP reply
    # code and enhanced status code.
    !/^([2-5][0-9][0-9]($|[- ]))/ 250-filler for garbage
</pre>

<p> This feature is available in Postfix 2.7. </p>

%PARAM lmtp_reply_filter

<p> The LMTP-specific version of the smtp_reply_filter
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.7 and later. </p>

%PARAM smtp_tls_block_early_mail_reply no

<p> Try to detect a mail hijacking attack based on a TLS protocol
vulnerability (CVE-2009-3555), where an attacker prepends malicious
HELO, MAIL, RCPT, DATA commands to a Postfix SMTP client TLS session.
The attack would succeed with non-Postfix SMTP servers that reply
to the malicious HELO, MAIL, RCPT, DATA commands after negotiating
the Postfix SMTP client TLS session.  </p>

<p> This feature is available in Postfix 2.7. </p>

%PARAM lmtp_tls_block_early_mail_reply

<p> The LMTP-specific version of the smtp_tls_block_early_mail_reply
configuration parameter.  See there for details. </p>

<p> This feature is available in Postfix 2.7 and later. </p>

%PARAM empty_address_default_transport_maps_lookup_key &lt;&gt;

<p> The sender_dependent_default_transport_maps search string that
will be used instead of the null sender address. </p>

<p> This feature is available in Postfix 2.7 and later.  </p>

%PARAM sender_dependent_default_transport_maps

<p> A sender-dependent override for the global default_transport
parameter setting. The tables are searched by the envelope sender
address and @domain. A lookup result of DUNNO terminates the search
without overriding the global default_transport parameter setting.
This information is overruled with the transport(5) table. </p>

<p> Note: this overrides default_transport, not transport_maps, and
therefore the expected syntax is that of default_transport, not the
syntax of transport_maps.  Specifically, this does not support the
transport_maps syntax for null transport, null nexthop, or null
email addresses. </p>

<p> For safety reasons, this feature does not allow $number
substitutions in regular expression maps. </p>

<p> This feature is available in Postfix 2.7 and later.  </p>

%PARAM address_verify_sender_dependent_default_transport_maps $sender_dependent_default_transport_maps

<p> Overrides the sender_dependent_default_transport_maps parameter
setting for address verification probes.  </p>

<p> This feature is available in Postfix 2.7 and later.  </p>

%PARAM default_filter_nexthop

<p> When a content_filter or FILTER request specifies no explicit
next-hop destination, use $default_filter_nexthop instead; when
that value is empty, use the domain in the recipient address.
Specify "default_filter_nexthop = $myhostname" for compatibility
with Postfix version 2.6 and earlier, or specify an explicit next-hop
destination with each content_filter value or FILTER action. </p>

<p> This feature is available in Postfix 2.7 and later.  </p>