libexec/spamd/spamd.8

.\"	$OpenBSD: spamd.8,v 1.35 2003/06/02 14:27:12 jmc Exp $
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.\" Copyright (c) 2002 Theo de Raadt.  All rights reserved.
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.Dd December 18, 2002
.Dt SPAMD 8
.Os
.Sh NAME
.Nm spamd
.Nd spam deferral daemon
.Sh SYNOPSIS
.Nm spamd
.Op Fl 45d
.Op Fl c Ar maxcon
.Op Fl n Ar name
.Op Fl p Ar port
.Op Fl r Ar reply
.Sh DESCRIPTION
.Nm
is a fake
.Xr sendmail 8 Ns -like
daemon which rejects false mail.
If the
.Xr pf 4
packet filter is configured to redirect port 25 (SMTP) to this daemon,
it will attempt to waste the time and resources of the spam sender.
.Pp
The options are as follows:
.Bl -tag -width Ds
.Pp
.It Fl 4
Return error code 450 to the spammer (default).
.It Fl 5
Return error code 550 to the spammer.
.It Fl c Ar maxcon
The maximum number of concurrent connections to allow.
The default is 200.
.It Fl d
Debug mode.
.Nm
does not
.Xr fork 2
into the background.
.It Fl n Ar name
The SMTP version banner that is reported upon initial connection.
.It Fl p Ar port
Specify a different port number from the default port that
.Nm
should listen for redirected SMTP connections on.
The default port is found by looking for the named service
.Em spamd
using
.Xr getservbyname 3 .
.It Fl r Ar reply
The SMTP error to return to the spammer, i.e. 450, 451, 550.
This defaults to 450.
.El
.Pp
.Nm
is designed to be very efficient so that it does not slow down the
receiving machine.
Spam is never accepted, but always rejected with either a 450 or 550
error message.
The normal way that spam has been dealt with in the past is to either
accept and drop, or outright block.
When configured to use 450 responses,
.Nm
takes neither of these actions: it rejects the mail back to the senders'
queue.
.Pp
.Nm
is best started from
.Xr rc 8
in conjunction with the
.Xr spamd-setup 8
which processes a list of spammers' addresses, and applies appropriate
.Xr pfctl 8
.Em rdr
rules.
.Xr spamd-setup 8
is run from
.Xr cron 8 .
.Sh REDIRECTING SMTP CONNECTIONS
With
.Xr pf 4 ,
connections to port 25 (SMTP) can be redirected to another host or port,
based on the source address of the sender.
The
.Em rdr
rules used for this purpose are described in
.Xr pf.conf 5 .
The rules can be loaded into a
.Em table
to simplify handling.
.Bd -literal
    table <spamd> persist
    rdr inet proto tcp from <spamd> to any port smtp -> 127.0.0.1 port 8025
.Ed
.Pp
Any addresses in table
.Em <spamd>
are then redirected to
.Nm
running on port 8025.
Addresses can be loaded into the
.Em table ,
like:
.Bd -literal
    # pfctl -q -t spamd -T replace -f /usr/local/share/spammers
.Ed
.Pp
.Xr spamd-setup 8
can also be used to load addresses into the
.Em <spamd>
table.
.Xr spamd-setup 8
also has the added benefit of being able to remove addresses from
blacklists, and will connect to
.Nm
over a localhost socket, giving
.Nm
information about each source of blacklist addresses, as well as custom
rejection messages for each blacklist source
that can be used to let any real person whose mail
is deferred by spamd know why their address has been listed
from sending mail.
This is important as it allows legitimate mail
senders to pressure spam sources into behaving properly so that they
may be removed from the relevant blacklists.
.Sh CONFIGURATION CONNECTIONS
.Nm
listens for configuration connections on the port identified by the
named service
.Em spamd-cfg
(see
.Xr services 5 ) .
The configuration socket listens only on the INADDR_LOOPBACK
address.
Configuration of spamd is done by connecting to the configuration
socket, and sending blacklist information, one blacklist per line.
Each blacklist consists of a name, a message to reject mail
with, and addresses in CIDR format, all separated by semicolons (;):
.Bd -literal
      tag;"rejection message";aaa.bbb.ccc.ddd/mm;aaa.bbb.ccc.ddd/mm
.Ed
.Pp
The rejection message must be inside double quotes.
A \e" will produce a double quote in the output.
\en will produce a newline.
%A will expand to the connecting IP address in dotted quad format.
%% may be used to produce a single % in the output.
\e\e will produce a single \e.
.Nm
will reject mail by displaying all the messages from all blacklists in which
a connecting address is matched.
.Xr spamd-setup 8
is normally used to configure this information.
.Sh FILES
/etc/spamd.conf
.Sh SEE ALSO
.Xr pf.conf 5 ,
.Xr services 5 ,
.Xr spamd.conf 5 ,
.Xr pfctl 8 ,
.Xr spamd-setup 8
.Sh HISTORY
The
.Nm
command
appeared in
.Ox 3.3 .