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Published by the Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

Copyright © 2005--2021 Sergey Poznyakoff

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license is included in the section entitled ``GNU Free Documentation License''.

     Dedico aquest treball a Lluis Llach, per obrir els nous horitzons.

Mailfromd
*********

This edition of the Mailfromd Manual, last updated UPDATED, documents mailfromd Version VERSION.

Preface
*******

Simple Mail Transfer Protocol (SMTP) which is the standard for email transmissions across the Internet was designed in the good old days when nobody could even think of the possibility of e-mail being abused to send tons of unsolicited messages of dubious contents.  Therefore it lacks mechanisms that could have prevented this abuse (spamming), or at least could have made it difficult.  Attempts to introduce such mechanisms (such as SMTP-AUTH extension (http://tools.ietf.org/html/rfc2554)) are being made, but they are not in wide use yet and, probably, their introduction will not be enough to stop the e-mail abuse.  Spamming is today's grim reality and developers spend lots of time and efforts designing new protection measures against it. Mailfromd is one of such attempts.

The package is designed to work with any MTA supporting Milter or Pmilter protocol, such as Sendmail, MeTA1 or Postfix.  It allows you to:

  * Control whether messages come from trustworthy senders, using so called callout or Sender Address Verification (see SAV) mechanism.

  * Prevent emails coming from forged addresses by use of SPF mechanism (see SPF Functions).

  * Limit connection and/or sending rates (see Rate Limit).

  * Use black-, white- and greylisting techniques.

  * Invoke external programs or other mail filters.

Short history of mailfromd.
===========================

The idea of the utility appeared in 2005, and its first version appeared soon afterward.  Back then it was a simple implementation of Sender Address Verification (see SAV) for Sendmail (hence its name -- mailfromd) with rudimentary tuning possibilities.

After a short run on my mail servers, I discovered that the utility was not flexible enough.  It took less than a month to implement a configuration file that allowed the user to control program and data flow during the envfrom SMTP state.  The new version, 1.0, appeared in June, 2005.

Next major release, 1.2 (1.1 contained mostly bugfixes), appeared two months later, and introduced mail sending rate control (see Rate Limit).

The program evolved during the next year, and the version 2.0 was released in September, 2006.  This version was a major change in the main idea of the program.  Configuration file become a flexible filter script allowing the operator to control almost all SMTP states.  The program supplied in the script file was compiled into a pseudo-code at startup, this code being subsequently evaluated each time the filter was invoked.  This caused a considerable speed-up in comparison with the previous versions, where the run-time evaluator was traversing the parse tree.  This version also introduced (implicitly, at the time), two separate data types for the entities declared in the script, which also played its role in the speed improvement (in the previous versions all data were considered strings).  Lots of improvements were made in the filter language (MFL, see MFL) itself, such as user-defined functions, the switch statement, the catch statement for handling run-time errors, etc.  The set of built-in functions extended considerably.  A testsuite (using DejaGNU) was introduced in this version.

During this initial development period the limitations imposed by libmilter implementation became obvious.  Finally, I felt they were stopping further development, and decided that mailfromd should use its own Milter implementation.  This new library, libgacopyz was the main new feature of the 3.0 release, which was released in November, 2006. Another major feature was the --dump-macros option and macros to rc.mailfromd script, that were intended to facilitate the configuration on Sendmail side.

The development of 3.x (more properly, 3.1.x) series concentrated mainly on bug-fixes, while the main development was done on the next branch.

The version 4.0 appeared on May 12, 2007.  A full list of changes in this release is more than 500 lines long, so it is impractical to list them here.  In particular, this version introduced lots of new features in MFL syntax and the library of useful MFL functions.  The runtime engine was also improved, in particular, stack space become expandable which eliminated many run-time errors.  This version also provided a foundation for MFL module system.  The code generation was re-implemented to facilitate introduction of object files in future versions.  Another new features in this release include SPF support and mtasim utility --- an MTA simulator designed for testing mailfromd scripts (see mtasim).  The test suite in this version was made portable by rewriting it in Autotest.

Another big leap forward was the 5.0 release, which appeared on December 26, 2008.  It largely enriched a set of available functions (61 new functions were introduced, which amounts to 41% of all the available functions in 5.0 release) and introduced several improvements in the MFL itself.  Among others, function aliases and optional arguments in user-defined functions were introduced in this release.  The new ``run operation mode'' allowed to execute arbitrary MFL functions from the command line.  This release also raised the Mailutils version requirements to at least 2.0.

Version 6.0, which was released in on 12 December, 2009, introduced a full-fledged modular system, akin to that of Python, and quite a few improvements to the language. such as explicit type casts, concatenation operator, static variables, etc.

Starting from version 7.0, the focus of further development of mailfromd has shifted.  While previously it had been regarded as a mail-filtering server, since then it was developed as a system for extending MTA functionality in the broad sense, mail filtering being only one of features it provides.

Version 7.0 makes the MFL syntax more consistent and the language itself more powerful.  For example, it is no longer necessary to use prefixes before variables to dereference them.  The new try--catch construct allows for elegant handling of exceptions and errors.  User-defined exceptions provide a way for programming complex loops and recursions with non-local exits.

This version introduces a concept of dedicated callout server. This allows mailfromd to defer verifications for a later time if the remote server does not response within a reasonably short period of time (see SMTP Timeouts).

Six years later the version 8.0 was released.  This version was a major rewrite of the mailfromd codebase.  It introduced a separate callout daemon that made it possible to separate the mailfromd server machine from machines performing callout checks.  The MFL language was extended by a number of built-in functions.

Since version 8.3 (2017-11-02) mailfromd uses adns (https://www.gnu.org/software/adns) for DNS queries.

The version 8.7 released in July, 2020 introduced DKIM support.

Acknowledgments
===============

Many people need to be thanked for their assistance in developing and debugging mailfromd.  After S. C. Johnson, I can say that this program ``owes much to a most stimulating collection of users, who have goaded me beyond my inclination, and frequently beyond my ability in their endless search for "one more feature".  Their irritating unwillingness to learn how to do things my way has usually led to my doing things their way; most of the time, they have been right.''

A real test for a program like mailfromd cannot be done but in conditions of production environment.  A decision to try it in these conditions is by no means an easy one, it requires courage and good faith in the intentions and abilities of the author.  To begin with, I would like to thank my contributors for these virtues.

Jan Rafaj has intrepidly been using mailfromd since its early releases and invested lots of efforts in improving the program and its documentation.  He is the author of many of the MFL library functions, shipped with the package.  Some of his ideas are still waiting in my implementation queue, while new ones are consistently arriving.

Peter Markeloff patiently tested every mailfromd release and helped discover and fix many bugs.

Zeus Panchenko contributed many ideas and gave lots of helpful comments.  He offered invaluable help in debugging and testing mailfromd on FreeBSD platform.

Sergey Afonin proposed many improvements and new ideas.  He also invested a lot of his time in finding bugs and testing bugfixes.

John McEleney and Ben McKeegan contributed the token bucket filter implementation (see TBF).

Con Tassios helped to find and fix various bugs and contributed the new implementation of the greylist function (see greylisting types).

The following people (in alphabetical order) provided bug reports and helpful comments for various versions of the program: Alan Dobkin, Brent Spencer, Jeff Ballard, Nacho González López, Phil Miller, Simon Christian, Thomas Lynch.

Introduction to mailfromd
*************************

Mailfromd is a general-purpose mail filtering daemon and a suite of accompanying utilities for Sendmail (See http://www.sendmail.org), MeTA1 (See http://www.meta1.org), Postfix (See http://www.postfix.org) or any other MTA that supports Milter (or Pmilter) protocol.  It is able to filter both incoming and outgoing messages using a filter program, written in mail filtering language (MFL).  The daemon interfaces with the MTA using Milter protocol.

The name mailfromd can be thought of as an abbreviation for Mail Filtering and Runtime Modification Daemon, with an o for itself. Historically, it stemmed from the fact that the original implementation was a simple filter implementing the sender address verification technique.  Since then the program has changed dramatically, and now it is actually a language translator and run-time evaluator providing a set of built-in and library functions for filtering electronic mail.

The first part of this manual is an overview, describing the features mailfromd offers in general.

The second part is a tutorial, which provides an introduction for those who have not used mailfromd previously.  It moves from topic to topic in a logical, progressive order, building on information already explained.  It offers only the principal information needed to master basic practical usage of mailfromd, while omitting many subtleties.

The other parts are meant to be used as a reference for those who know mailfromd well enough, but need to look up some notions from time to time.  Each chapter presents everything that needs to be said about a specific topic.

The manual assumes that the reader has a good knowledge of the SMTP protocol and the mail transport system he uses (Sendmail , Postfix or MeTA1).

Typographical conventions
=========================

This manual is written using Texinfo, the GNU documentation formatting language.  The same set of Texinfo source files is used to produce both the printed and online versions of the documentation. This section briefly documents the typographical conventions used in this manual.

Examples you would type at the command line are preceded by the common shell primary prompt, $.  The command itself is printed in this font, and the output it produces in this font, for example:

     $ mailfromd --version
     mailfromd (mailfromd VERSION)

In the text, the command names are printed like this, command line options are displayed in this font.  Some notions are emphasized like this, and if a point needs to be made strongly, it is done this way.  The first occurrence of a new term is usually its definition and appears in the same font as the previous occurrence of ``definition'' in this sentence. File names are indicated like this: /path/to/ourfile.

The variable names are represented LIKE THIS, keywords and fragments of program text are written in this font.

Overview of Mailfromd
=====================

In contrast to the most existing milter filters, mailfromd does not implement any default filtering policies.  Instead, it depends entirely on a filter script, supplied to it by the administrator.  The script, written in a specialized and simple to use language, called MFL (see MFL), is supposed to run a set of tests and to decide whether the message should be accepted by the MTA or not. To perform the tests, the script can examine the values of Sendmail macros, use an extensive set of built-in and library functions, and invoke user-defined functions.

Sender Address Verification.
============================

Sender address verification, or callout, is one of the basic mail verification techniques, implemented by mailfromd.  It consists in probing each MX server for the given address, until one of them gives a definite (positive or negative) reply.  Using this technique you can block a sender address if it is not deliverable, thereby cutting off a large amount of spam. It can also be useful to block mail for undeliverable recipients, for example on a mail relay host that does not have a list of all the valid recipient addresses.  This prevents undeliverable junk mail from entering the queue, so that your MTA doesn't have to waste resources trying to send MAILER-DAEMON messages back.

Let's illustrate how it works on an example:

Suppose that the user <jsmith@somedomain.net> is trying to send mail to one of your local users.  The remote machine connects to your MTA and issues MAIL FROM: <jsmith@somedomain.net> command.  However, your MTA does not have to take its word for it, so it uses mailfromd to verify the sender address validity.  Mailfromd strips the domain name from the address (somedomain.net) and queries DNS about MX records for that domain.  Suppose, it receives the following list

10   relay1.somedomain.net
20   relay2.somedomain.net

It then connects to first MX server, using SMTP protocol, as if it were going to send a message to <jsmith@somedomain.net>.  This is called sending a probe message.  If the server accepts the recipient address, the mailfromd accepts the incoming mail.  Otherwise, if the server rejects the address, the mail is rejected as well.  If the MX server cannot be connected, mailfromd selects next server from the list and continues this process until it finds the answer or the list of servers is exhausted.

The probe message is like a normal mail except that no data are ever being sent.  The probe message transaction in our example might look as follows (S: meaning messages sent by remote MTA, C: meaning those sent by mailfromd):

     C: HELO mydomain.net
     S: 220 OK, nice to meet you
     C: MAIL FROM: <>
     S: 220 <>: Sender OK
     C: RCPT TO: <jsmith@somedomain.net>
     S: 220 <jsmith@remote.net>: Recipient OK
     C: QUIT

Probe messages are never delivered, deferred or bounced; they are always discarded.

The described method of address verification is called a standard method throughout this document.  Mailfromd also implements a method we call strict.  When using strict method, mailfromd first resolves IP address of sender machine to a fully qualified domain name.  Then it obtains MX records for this machine, and then proceeds with probing as described above.

So, the difference between the two methods is in the set of MX records that are being probed: standard method queries MXs based on the sender email domain, strict method works with MXs for the sender IP address.

Strict method allows to cut off much larger amount of spam, although it does have many drawbacks.  Returning to our example above, consider the following situation: <jsmith@somedomain.net> is a perfectly normal address, but it is being used by a spammer from some other domain, say otherdomain.com.  The standard method is not able to cope with such cases, whereas the strict one is.

An alert reader will ask: what happens if mailfromd is not able to get a definite answer from any of MX servers?  Actually, it depends entirely on how you will instruct it to act in this case, but the general practice is to return temporary failure, which will urge the remote party to retry sending their message later.

After receiving a definite answer, mailfromd will cache it in its database, so that next time your MTA receives a message from that address (or from the sender IP/email address pair, for strict method), it will not waste its time trying to reach MX servers again.  The records remain in the cache database for a certain time, after which they are discarded.

Limitations of Sender Address Verification
------------------------------------------

Before deciding whether and how to use sender address verification, you should be aware of its limitations.

Both standard and strict methods suffer from the following limitations:

  * The sender verification methods will perform poorly on highly loaded sites.  The traffic and/or resource usage overhead may not be feasible for you.  However, you may experiment with various mailfromd options to find an optimal configuration.

  * Some sites may blacklist your MTA if it probes them too often.  Mailfromd eliminates this drawback by using a cache database, which keeps results of the recent callouts.

  * When verifying the remote address, no attempt to actually deliver the message is made.  If MTA accepts the address, mailfromd assumes it is OK.  However in reality, a mail for a remote address can bounce after the nearest MTA accepts the recipient address.

     This drawback can often be avoided by combining sender address verification with greylisting (see Greylisting).

  * If the remote server rejects the address, no attempt is being made to discern between various reasons for rejection (client rejected, HELO rejected, MAIL FROM rejected, etc.)

  * Some major sites such as yahoo.com do not reject unknown addresses in reply to the RCPT TO command, but report a delivery failure in response to end of DATA after a message is transferred.  Of course, sender address verification does not work with such sites.  However, a combination of address verification and greylisting (see Greylisting) may be a good choice in such cases.

In addition, strict verification breaks forward mail delivery.  This is obvious, since mail forwarding is based on delivering unmodified message to another location, so the sender address domain will most probably not be the same as that of the MTA doing the forwarding.

Controlling Mail Sending Rate.
==============================

Mail Sending Rate for a given identity is defined as the number of messages with this identity received within a predefined interval of time.

MFL offers a set of functions for limiting mail sending rate (see Rate limiting functions), and for controlling broader rate aspects, such as data transfer rates (see TBF).

SPF, DKIM, and others
=====================

Sender Policy Framework, or SPF for short, is an extension to SMTP protocol that allows to identify forged identities supplied with the MAIL FROM and HELO commands.  The framework is explained in detail in RFC 4408 (http://tools.ietf.org/html/rfc4408) and on the SPF Project Site (http://www.openspf.org/).

Mailfromd provides a set of functions for using SPF to control mail flow.  These are described in SPF Functions.

DomainKeys Identified Mail (DKIM) is an email authentication method designed to detect forged sender addresses in emails.  Mailfromd supports both DKIM signing and verification.  See DKIM, for a detailed description of these features.

Mailfromd also provides support for several third-party spam-abatement programs, in particular SpamAssassin, ClamAV, and DSPAM.  These are discussed in Interfaces to Third-Party Programs.

Building the Package
********************

This chapter contains a detailed list of steps you need to undertake in order to configure and build the package.

 1. Make sure you have the necessary software installed.

     To build mailfromd you will need to have following packages on your machine:

      A. GNU mailutils version 3.3 or newer.

          GNU mailutils is a general-purpose library for handling electronic mail. It is available from http://mailutils.org.

      B. GNU adns library, version 1.5.1 or newer.

          GNU adns is an advanced DNS client library.  The recent version can be downloaded from http://www.chiark.greenend.org.uk/~ian/adns/adns.tar.gz. Visit http://www.gnu.org/software/adns, for more information.

      C. A DBM library. Mailfromd is able to link with any flavor of DBM supported by GNU mailutils.  As of version VERSION it will refuse to build without DBM. By default, configure will try to find the best implementation installed on your machine (preference is given to Berkeley DB) and will use it.  You can, however, explicitly specify which implementation you want to use.  To do so, use the --with-dbm configure option. Its argument specifies the type of database to use. It must be one of the types supported by GNU mailutils. At the time of this writing, these are:

          bdb
               Berkeley DB (versions 2 to 6).

          gdbm
               GNU DBM.

          kc
               Kyoto Cabinet

          tc
               Tokyo Cabinet

          ndbm
               NDBM

          To check what database types are supported by your version of mailutils, run the following command:

               $ mailutils dbd gdbm kc tc ndbm

          For backward compatibility, configure accepts the following two options:

          --with-gdbm
               Same as --with-dbm=gdbm.

          --with-berkeley-db
               Same as --with-dbm=bdb.

          For Sendmail users, it often makes sense to configure mailfromd to use the same database flavor as sendmail. The following table will help you do that.  The column DB type lists types of DBM databases supported by mailfromd. The column confMAPDEF lists the value of confMAPDEF Sendmail configuration macro corresponding to that database type. The column configure option contains the corresponding option to configure.

          DB type   confMAPDEF   configure option
          NDBM          -NNDBM       --with-dbm=ndbm
          Berkeley DB   -NNEWDB      --with-dbm=bdb
          GDBM          N/A                   --with-dbm=gdbm

 2. Decide what user privileges will be used to run mailfromd

     After startup, the program drops root privileges.  By default, it switches to the privileges of user mail, group mail. If there is no such user on your system, or you wish to use another user account for this purpose, override it using DEFAULT_USER environment variable.  For example for mailfromd to run as user nobody, use

          ./configure DEFAULT_USER=nobody

     The user name can also be changed at run-time (see --user).

 3. Decide where to install mailfromd and where its filter script and data files will be located.

     As usual, the default value for the installation prefix is /usr/local.  If it does not suit you, specify another location using --prefix option, e.g.: --prefix=/usr.

     During installation phase, the build system will install several files.  These files are:

     PREFIX/sbin/mailfromd
          Main daemon.  See mailfromd.

     PREFIX/etc/mailfromd.mf
          Default main filter script file.  It is installed only if it is not already there.  Thus, if you are upgrading to a newer version of mailfromd, your old script file will be preserved with all your changes.

          See MFL, for a description of the mail filtering language.

     PREFIX/share/mailfromd/VERSION/*.mf
          MFL modules.  See Modules.

     PREFIX/info/mailfromd.info*
          Documentation files.

     PREFIX/bin/mtasim
          MTA simulator program for testing mailfromd scripts.  See mtasim.

     PREFIX/sbin/pmult
          Pmilter multiplexor for MeTA1.  See pmult. It is build only if MeTA1 version PreAlpha29.0 or newer is installed on the system.  You may disable it by using the --disable-pmilter command line option.

          When testing for MeTA1 presence, configure assumes its default location.  If it is not found there, inform configure about its actual location by using the following option:

               --enable-pmilter=PREFIX

          where PREFIX stands for the MeTA1 installation prefix.

     It is advisable to use the same settings for file name prefixes as those you used when configuring mailutils.  In particular, try to use the same --sysconfdir, since it will facilitate configuring the whole system.

     Another important point is location of local state directory, i.e. a directory where mailfromd keeps its data files (e.g. communication socket, PID-file and database files).  By default, its full name is LOCALSTATEDIR/mailfromd.  You can change it by setting DEFAULT_STATE_DIR configuration variable.  This value can be changed at run-time using the state-directory configuration statement (see state-directory).

 4. Select default communication socket. This is the socket used to communicate with MTA, in the usual Milter port notation (see milter port specification). If the socket name does not begin with a protocol or directory separator, it is assumed to be a UNIX socket, located in the local state directory.  The default value is mailfrom, which is equivalent to unix:LOCALSTATEDIR/mailfromd/mailfrom.

     To alter this, use DEFAULT_SOCKET environment variable, e.g.:

          ./configure DEFAULT_SOCKET=inet:999@localhost

     The communication socket can be changed at run time using --port command line option (see --port) or the listen configuration statement (see listen).

 5. Select default expiration interval. Expiration interval defines the period of time during which a record in the mailfromd database is considered valid.  It is described in more detail in Databases.  The default value is 86400 seconds, i.e. 24 hours.  It is OK for most sites.  If, however, you wish to change it, use DEFAULT_EXPIRE_INTERVAL environment variable.

     The DEFAULT_EXPIRE_RATES_INTERVAL variable sets default expiration time for mail rate database (see Rate limiting functions).

     Expiration settings can be changed at run time using database statement in the mailfromd configuration file (see conf-database).

 6. Select a syslog implementation to use.

     Mailfromd uses syslog for diagnostics output.  The default syslog implementation on most systems (most notably, on GNU/Linux) uses blocking AF_UNIX SOCK_DGRAM sockets.  As a result, when an application calls syslog(), and syslogd is not responding and the socket buffers get full, the application will hang.

     For mailfromd, as for any daemon, it is more important that it continue to run, than that it continue to log.  For this purpose, mailfromd is shipped with a non-blocking syslog implementation by Simon Kelley.  This implementation, instead of blocking, buffers log lines in memory.  When the buffer log overflows, some lines are lost, but the daemon continues to run.  When lines are lost, this fact is logged with a message of the form:

             async_syslog overflow: 5 log entries lost

     To enable this implementation, configure the package with --enable-syslog-async option, e.g.:

          ./configure --enable-syslog-async

     Additionally, you can instruct mailfromd to use asynchronous syslog by default.  To do so, set DEFAULT_SYSLOG_ASYNC to 1, as shown in example below:

          ./configure --enable-syslog-async DEFAULT_SYSLOG_ASYNC=1

     You will be able to override these defaults at run-time by using the --logger command line option (see Logging and Debugging).

 7. Run configure with all the desired options.

     For example, the following command:

          ./configure DEFAULT_SOCKET=inet:999@localhost --with-berkeley-db=3

     will configure the package to use Berkeley DB database, version 2, and inet:999@localhost as the default communication socket.

     At the end of its run configure will print a concise summary of its configuration settings.  It looks like that (with the long lines being split for readability):

          *******************************************************************
          Mailfromd configured with the following settings:

          External preprocessor..................... /usr/bin/m4 -s
          DBM version............................... Berkeley DB v. 3
          Default user.............................. mail
          State directory...........................
                     $(localstatedir)/$(PACKAGE)
          Socket.................................... mailfrom
          Expiration interval....................... 86400
          Negative DNS answer expiration interval... 3600
          Rates expire interval..................... 300
          Default syslog implementation............. blocking
          Readline (for mtasim)..................... yes
          Documentation rendition type.............. PROOF
          Enable pmilter support.................... no
          Enable GeoIP support...................... no
          *******************************************************************

     Make sure these settings satisfy your needs.  If they do not, reconfigure the package with the right options.

 8. Run make.

 9. Run make install.

 10. Make sure LOCALSTATEDIR/mailfromd has the right owner and mode.

 11. Examine filter script file (SYSCONFDIR/mailfromd.mf) and edit it, if necessary.

 12. If you are upgrading from an earlier release of Mailfromd, refer to Upgrading, for detailed instructions.

Tutorial
********

This chapter contains a tutorial introduction, guiding you through various mailfromd configurations, starting from the simplest ones and proceeding up to more advanced forms.  It omits most complicated details, concentrating mainly on the common practical tasks.

If you are familiar to mailfromd, you can skip this chapter and go directly to the next one (see MFL), which contains detailed discussion of the mail filtering language and mailfromd interaction with the Mail Transport Agent.

Start Up
========

The mailfromd utility runs as a standalone daemon program and listens on a predefined communication channel for requests from the Mail Transfer Agent (MTA, for short).  When processing each message, the MTA installs communication with mailfromd, and goes through several states, collecting the necessary data from the sender.  At each state it sends the relevant information to mailfromd, and waits for it to reply.  The mailfromd filter receives the message data through Sendmail macros and runs a handler program defined for the given state.  The result of this run is a response code, that it returns to the MTA.  The following response codes are defined:

continue
     Continue message processing.

accept
     Accept this message for delivery.  After receiving this code the MTA continues processing this message without further consulting mailfromd filter.

reject
     Reject this message.  The message processing stops at this stage, and the sender receives the reject reply (5XX reply code).  No further mailfromd handlers are called for this message.

discard
     Silently discard the message.  This means that MTA will continue processing this message as if it were going to deliver it, but will discard it after receiving.  No further interaction with mailfromd occurs.

tempfail
     Temporarily reject the message.  The message processing stops at this stage, and the sender receives the temporary failure reply (4XX reply code).  No further mailfromd handlers are called for this message.

The instructions on how to process the message are supplied to mailfromd in its filter script file.  It is normally called /usr/local/etc/mailfromd.mf (but can be located elsewhere, see Invocation) and contains a set of milter state handlers, or subroutines to be executed in various SMTP states.  Each interaction state can be supplied its own handling procedure.  A missing procedure implies continue response code.

The filter script can define up to nine milter state handlers, called after the names of milter states: connect, helo, envfrom, envrcpt, data, header, eoh, body, and eom.  The data handler is invoked only if MTA uses Milter protocol version 3 or later.  Two special handlers are available for initialization and clean-up purposes: begin is called before the processing starts, and end is called after it is finished.  The diagram below shows the control flow when processing an SMTP transaction.  Lines marked with C: show SMTP commands issued by the remote machine (the client), those marked with => show called handlers with their arguments.  An [R] appearing at the start of a line indicates that this part of the transaction can be repeated any number of times:

Figure: Mailfromd Control Flow

     => begin()
     => connect(HOSTNAME, FAMILY, PORT, IP address)
     C: HELO DOMAIN
     helo(DOMAIN)
     for each message transaction
     do
             C: MAIL FROM SENDER
             => envfrom(SENDER)

     [R]     C: RCPT TO RECIPIENT
             => envrcpt(RECIPIENT)

             C: DATA
             => data()
     [R]     C: HEADER: VALUE
             => header(HEADER, VALUE)

             C:
             => eoh()

     [R]     C: BODY-LINE
             => /* Collect lines into blocks BLK of
             =>  * at most LEN bytes and for each
             =>  * such block call:
             =>  */
             => body(BLK, LEN)

             C: .
             => eom()
     done
     => end()

This control flow is maintained for as long as each called handler returns continue (see Actions).  Otherwise, if any handler returns accept or discard, the message processing continues, but no other handler is called.  In the case of accept, the MTA will accept the message for delivery, in the case of discard it will silently discard it.

If any of the handlers returns reject or tempfail, the result depends on the handler.  If this code is returned by envrcpt handler, it causes this particular recipient address to be rejected.  When returned by any other handler, it causes the whole message will be rejected.

The reject and tempfail actions executed by helo handler do not take effect immediately.  Instead, their action is deferred until the next SMTP command from the client, which is usually MAIL FROM.

Simplest Configurations
=======================

The mailfromd script file contains a series of declarations of the handler procedures.  Each declaration has the form:

     prog NAME
     do
       ...
     done

where prog, do and done are the keywords, and NAME is the state name for this handler.  The dots in the above example represent the actual code, or a set of commands, instructing mailfromd how to process the message.

For example, the declaration:

     prog envfrom
     do
       accept
     done

installs a handler for envfrom state, which always approves the message for delivery, without any further interaction with mailfromd.

The word accept in the above example is an action. Action is a special language statement that instructs the run-time engine to stop execution of the program and to return a response code to the Sendmail.  There are five actions, one for each response code: continue, accept, reject, discard, and tempfail.  Among these, reject and discard can optionally take one to three arguments.  There are two ways of supplying the arguments.

In the first form, called literal or traditional notation, the arguments are supplied as additional words after the action name, separated by whitespace.  The first argument is a three-digit RFC 2821 reply code.  It must begin with 5 for reject and with 4 for tempfail.  If two arguments are supplied, the second argument must be either an extended reply code (RFC 1893/2034) or a textual string to be returned along with the SMTP reply.  Finally, if all three arguments are supplied, then the second one must be an extended reply code and the third one must supply the textual string.  The following examples illustrate all possible ways of using the reject statement in literal notation:

     reject
     reject 503
     reject 503 5.0.0
     reject 503 "Need HELO command"
     reject 503 5.0.0 "Need HELO command"

Please note the quotes around the textual string.

Another form for these action is called functional notation, because it resembles the function syntax.  When used in this form, the action word is followed by a parenthesized group of exactly three arguments, separated by commas.  The meaning and ordering of the argument is the same as in literal form.  Any of three arguments may be absent, in which case it will be replaced by the default value.  To illustrate this, here are the statements from the previous example, written in functional notation:

     reject(,,)
     reject(503,,)
     reject(503, 5.0.0)
     reject(503,, "Need HELO command")
     reject(503, 5.0.0, "Need HELO command")

Conditional Execution
=====================

Programs consisting of a single action are rarely useful.  In most cases you will want to do some checking and decide whether to process the message depending on its result.  For example, if you do not want to accept messages from the address <badguy@some.net>, you could write the following program:

     prog envfrom
     do
       if $f = "badguy@some.net"
         reject
       else
         accept
       fi
     done

This example illustrates several important concepts.  First or all, $f in the third line is a Sendmail macro reference.  Sendmail macros are referenced the same way as in sendmail.cf, with the only difference that curly braces around macro names are optional, even if the name consists of several letters.  The value of a macro reference is always a string.

The equality operator (=) compares its left and right arguments and evaluates to true if the two strings are exactly the same, or to false otherwise.  Apart from equality, you can use the regular relational operators: !=, >, >=, < and <=.  Notice that string comparison in mailfromd is always case sensitive.  To do case-insensitive comparison, translate both operands to upper or lower case (see tolower, and see toupper).

The if statement decides what actions to execute depending on the value its condition evaluates to.  Its usual form is:

     if EXPRESSION THEN-BODY [else ELSE-BODY] fi

The THEN-BODY is executed if the EXPRESSION evaluates to true (i.e. to any non-zero value).  The optional ELSE-BODY is executed if the EXPRESSION yields false (i.e. zero).  Both THEN-BODY and ELSE-BODY can contain other if statements, their nesting depth is not limited.  To facilitate writing complex conditional statements, the elif keyword can be used to introduce alternative conditions, for example:

     prog envfrom
     do
       if $f = "badguy@some.net"
         reject
       elif $f = "other@domain.com"
         tempfail 470 "Please try again later"
       else
         accept
       fi
     done

See switch, for more elaborate forms of conditional branching.

Functions and Modules
=====================

As any programming language, MFL supports a concept of function, i.e. a body of code that is assigned a unique name and can be invoked elsewhere as many times as needed.

All functions have a definition that introduces types and names of the formal parameters and the result type, if the function is to return a meaningful value (function definitions in MFL are discussed in detail in see User-Defined Functions).

A function is invoked using a special construct, a function call:

      NAME (ARG-LIST)

where NAME is the function name, and ARG-LIST is a comma-separated list of expressions.  Each expression in ARG-LIST is evaluated, and its type is compared with that of the corresponding formal argument.  If the types differ, the expression is converted to the formal argument type.  Finally, a copy of its value is passed to the function as a corresponding argument.  The order in which the expressions are evaluated is not defined.  The compiler checks that the number of elements in ARG-LIST match the number of mandatory arguments for function NAME.

If the function does not deliver a result, it should only be called as a statement.

Functions may be recursive, even mutually recursive.

Mailfromd comes with a rich set of predefined functions for various purposes.  There are two basic function classes: built-in functions, that are implemented by the MFL runtime environment in mailfromd, and library functions, that are implemented in MFL.  The built-in functions are always available and no preparatory work is needed before calling them.  In contrast, the library functions are defined in modules, special MFL source files that contain functions designed for a particular task.  In order to access a library function, you must first require a module it is defined in. This is done using require statement.  For example, the function hostname looks up in the DNS the name corresponding to the IP address specified as its argument.  This function is defined in module dns.mf, so before calling it you must require this module:

     require dns

The require statement takes a single argument: the name of the requested module (without the .mf suffix).  It looks up the module on disk and loads it if it is available.

For more information about the module system see Modules.

Domain Name System
==================

Site administrators often do not wish to accept mail from hosts that do not have a proper reverse delegation in the Domain Name System. In the previous section we introduced the library function hostname, that looks up in the DNS the name corresponding to the IP address specified as its argument.  If there is no corresponding name, the function returns its argument unchanged.  This can be used to test if the IP was resolved, as illustrated in the example below:

     require 'dns'

     prog envfrom
     do
       if hostname($client_addr) = $client_addr
         reject
       fi
     done

The #require dns statement loads the module dns.mf, after which the definition of hostname becomes available.

A similar function, resolve, which resolves the symbolic name to the corresponding IP address is provided in the same dns.mf module.

Checking Sender Address
=======================

A special language construct is provided for verification of sender addresses (callout):

     on poll $f do
     when success:
       accept
     when not_found or failure:
       reject 550 5.1.0 "Sender validity not confirmed"
     when temp_failure:
       tempfail 450 4.1.0 "Try again later"
     done

The on poll construct runs standard verification (see standard verification) for the email address specified as its argument (in the example above it is the value of the Sendmail macro $f).  The check can result in the following conditions:

success
     The address exists.

not_found
     The address does not exist.

failure
     Some error of permanent nature occurred during the check.  The existence of the address cannot be verified.

temp_failure
     Some temporary failure occurred during the check.  The existence of the address cannot be verified at the moment.

The when branches of the on poll statement introduce statements, that are executed depending on the actual return condition.  If any condition occurs that is not handled within the on block, the run-time evaluator will signal an exception (For more information about exceptions and their handling, please refer to Exceptions.) and return temporary failure, therefore it is advisable to always handle all four conditions.  In fact, the condition handling shown in the above example is preferable for most normal configurations: the mail is accepted if the sender address is proved to exist and rejected otherwise.  If a temporary failure occurs, the remote party is urged to retry the transaction some time later.

The poll statement itself has a number of options that control the type of the verification.  These are discussed in detail in poll.

It is worth noticing that there is one special email address which is always available on any host, it is the null address <> used in error reporting.  It is of no use verifying its existence:

     prog envfrom
     do
       if $f == ""
         accept
       else
         on poll $f do
         when success:
           accept
         when not_found or failure:
           reject 550 5.1.0 "Sender validity not confirmed"
         when temp_failure:
           tempfail 450 4.1.0 "Try again later"
         done
       fi
     done

SMTP Timeouts
=============

When using polling functions, it is important to take into account possible delays, which can occur in SMTP transactions.  Such delays may be due to low network bandwidth or high load on the remote server.  Some sites impose them willingly, as a spam-fighting measure.

Ideally the callout verification should use the timeout values defined in the RFC 2822, but this is impossible in practice, because it would cause a timeout escalation, which consists in propagating delays encountered in a callout SMTP session back to the remote client whose session initiated the callout.

Consider, for example, the following scenario.  An MFL script performs a callout on envfrom stage.  The remote server is overloaded and delays heavily in responding, so that the initial response arrives 3 minutes after establishing the connection, and processing the EHLO command takes another 3 minutes.  These delays are OK according to the RFC, which imposes a 5 minute limit for each stage, but while waiting for the remote reply our SMTP server remains in the envfrom state with the client waiting for a response to its MAIL command more than 6 minutes, which is intolerable, because of the same 5 minute limit.  Thus, the client will almost certainly break the session.

To avoid this, mailfromd uses a special instance, called callout server, which is responsible for running callout SMTP sessions asynchronously.  The usual sender verification is performed using so-called soft timeout values, which are set to values short enough to not disturb the incoming session (e.g. a timeout for HELO response is 3 seconds, instead of 5 minutes).  If this verification yields a definite answer, that answer is stored in the cache database and returned to the calling procedure immediately.  If, however, the verification is aborted due to a timeout, the caller procedure is returned an e_temp_failure exception, and the callout is scheduled for processing by a callout server.  This exception normally causes the milter session to return a temporary error to the sender, urging it to retry the connection later.

In the meantime, the callout server runs the sender verification again using another set of timeouts, called hard timeouts, which are normally much longer than soft ones (they default to the values required by RFC 2822).  If it gets a definitive result (e.g. email found or email not found), the server stores it in the cache database.  If the callout ends due to a timeout, a not_found result is stored in the database.

Some time later, the remote server retries the delivery, and the mailfromd script is run again.  This time, the callout function will immediately obtain the already cached result from the database and proceed accordingly.  If the callout server has not finished the request by the time the sender retries the connection, the latter is again returned a temporary error, and the process continues until the callout is finished.

Usually, callout server is just another instance of mailfromd itself, which is started automatically to perform scheduled SMTP callouts.  It is also possible to set up a separate callout server on another machine.  This is discussed in calloutd.

For a detailed information about callout timeouts and their configuration, see conf-timeout.

For a description of how to configure mailfromd to use callout servers, see conf-server.

Avoiding Verification Loops
===========================

An envfrom program consisting only of the on poll statement will work smoothly for incoming mails, but will create infinite loops for outgoing mails.  This is because upon sending an outgoing message mailfromd will start the verification procedure, which will initiate an SMTP transaction with the same mail server that runs it.  This transaction will in turn trigger execution of on poll statement, etc.  ad infinitum.  To avoid this, any properly written filter script should not run the verification procedure on the email addresses in those domains that are relayed by the server it runs on.  This can be achieved using relayed function.  The function returns true if its argument is contained in one of the predefined domain list files.  These files correspond to Sendmail plain text files used in F class definition forms (see Sendmail Installation and Operation Guide, chapter 5.3), i.e. they contain one domain name per line, with empty lines and lines started with # being ignored. The domain files consulted by relayed function are defined in the relayed-domain-file configuration file statement (see relayed-domain-file):

     relayed-domain-file (/etc/mail/local-host-names,
                          /etc/mail/relay-domains);

or:

     relayed-domain-file /etc/mail/local-host-names;
     relayed-domain-file /etc/mail/relay-domains;

The above example declares two domain list files, most commonly used in Sendmail installations to keep hostnames of the server (class w, see Sendmail Installation and Operation Guide, chapter 5.2.) and names of the domains, relayed by this server (class R).

Given all this, we can improve our filter program:

     require 'dns'

     prog envfrom
     do
       if $f == ""
         accept
       elif relayed(hostname(${client_addr}))
         accept
       else
         on poll $f do
         when success:
           accept
         when not_found or failure:
           reject 550 5.1.0 "Sender validity not confirmed"
         when temp_failure:
           tempfail 450 4.1.0 "Try again later"
         done
       fi
     done

If you feel that your Sendmail's relayed domains are not restrictive enough for mailfromd filters (for example you are relaying mails from some third-party servers), you can use a database of trusted mail server addresses.  If the number of such servers is small enough, a single or statement can be used, e.g.:

       elif ${client_addr} = "10.10.10.1"
            or ${client_addr} = "192.168.11.7"
         accept
       ...

otherwise, if the servers' IP addresses fall within one or several CIDRs, you can use the match_cidr function (see Internet address manipulation functions), e.g.:

       elif match_cidr (${client_addr}, "199.232.0.0/16")
         accept
       ...

or combine both methods.  Finally, you can keep a DBM database of relayed addresses and use dbmap or dbget function for checking (see Database functions).

       elif dbmap("%__statedir__/relay.db", ${client_addr})
         accept
       ...

HELO Domain
===========

Some of the mail filtering conditions may depend on the value of helo domain name, i.e. the argument to the SMTP EHLO (or HELO) command.  If you ever need such conditions, take into account the following caveats.  Firstly, although Sendmail passes the helo domain in $s macro, it does not do this consistently.  In fact, the $s macro is available only to the helo handler, all other handlers won't see it, no matter what the value of the corresponding Milter.macros.HANDLER statement.  So, if you wish to access its value from any handler, other than helo, you will have to store it in a variable in the helo handler and then use this variable value in the other handler.  This approach is also recommended for another MTAs.  This brings us to the concept of variables in mailfromd scripts.

A variable is declared using the following syntax:

     TYPE NAME

where VARIABLE is the variable name and TYPE is string, if the variable is to hold a string value, and number, if it is supposed to have a numeric value.

A variable is assigned a value using the set statement:

     set NAME EXPR

where EXPR is any valid MFL expression.

The set statement can occur within handler or function declarations as well as outside of them.

There are two kinds of Mailfromd variables: global variables, that are visible to all handlers and functions, and automatic variables, that are available only within the handler or function where they are declared.  For our purpose we need a global variable (see Variable classes, for detailed descriptions of both kinds of variables).

The following example illustrates an approach that allows to use the HELO domain name in any handler:

     # Declare the helohost variable
     string helohost

     prog helo
     do
       # Save the host name for further use
       set helohost $s
     done

     prog envfrom
     do
       # Reject hosts claiming to be localhost
       if helohost = "localhost"
         reject 570 "Please specify real host name"
       fi
     done

Notice, that for this approach to work, your MTA must export the s macro (e.g., in case of Sendmail, the Milter.macros.helo statement in the sendmail.cf file must contain s.  see Sendmail).  This requirement can be removed by using the handler argument of helo.  Each mailfromd handler is given one or several arguments.  The exact number of arguments and their meaning are handler-specific and are described in Handlers, and milter-control-flow. The arguments are referenced by their ordinal number, using the notation $N.  The helo handler takes one argument, whose value is the helo domain.  Using this information, the helo handler from the example above can be rewritten as follows:

     prog helo
     do
       # Save the host name for further use
       set helohost $1
     done

SMTP RSET and Milter Abort Handling
===================================

In previous section we have used a global variable to hold certain information and share it between handlers.  In the majority of cases, such information is session specific, and becomes invalid if the remote party issues the SMTP RSET command.  Therefore, mailfromd clears all global variables when it receives a Milter abort request, which is normally generated by this command.

However, you may need some variables that retain their values even across SMTP session resets.  In mailfromd terminology such variables are called precious.  Precious variables are declared by prefixing their declaration with the keyword precious.  Consider, for example, this snippet of code:

     precious number rcpt_counter

     prog envrcpt
     do
       set rcpt_counter rcpt_counter + 1
     done

Here, the variable rcpt_counter is declared as precious and its value is incremented each time the envrcpt handler is called.  This way, rcpt_counter will keep the total number of SMTP RCPT commands issued during the session, no matter how many times it was restarted using the RSET command.

Controlling Number of Recipients
================================

Any MTA provides a way to limit the number of recipients per message.  For example, in Sendmail you may use the MaxRecipientsPerMessage option (Sendmail (tm) Installation and Operation Guide, chapter 5.6, O -- Set Option.).  However, such methods are not flexible, so you are often better off using mailfromd for this purpose.

Mailfromd keeps the number of recipients collected so far in variable rcpt_count, which can be controlled in envrcpt handler as shown in the example below:

     prog envrcpt
     do
       if rcpt_count > 10
         reject 550 5.7.1 "Too many recipients"
       fi
     done

This filter will accept no more than 10 recipients per message. You may achieve finer granularity by using additional conditions.  For example, the following code will allow any number of recipients if the mail is coming from a domain relayed by the server, while limiting it to 10 for incoming mail from other domains:

     prog envrcpt
     do
       if not relayed(hostname($client_addr)) and rcpt_count > 10
         reject 550 5.7.1 "Too many recipients"
       fi
     done

There are three important features to notice in the above code. First of all, it introduces two boolean operators: and, which evaluates to true only if both left-side and right-side expressions are true, and not, which reverses the value of its argument.

Secondly, the scope of an operation is determined by its precedence, or binding strength.  Not binds more tightly than and, so its scope is limited by the next expression between it and and.  Using parentheses to underline the operator scoping, the above if condition can be rewritten as follows:

         if (not (relayed(hostname($client_addr)))) and (%rcpt_count > 10)

Finally, it is important to notice that all boolean expressions are computed using shortcut evaluation.  To understand what it is, let's consider the following expression: X and Y.  Its value is true only if both X and Y are true.  Now suppose that we evaluate the expression from left to right and we find that X is false.  This means that no matter what the value of Y is, the resulting expression will be false, therefore there is no need to compute Y at all. So, the boolean shortcut evaluation works as follows:

X and Y
     If X => false, do not evaluate Y and return false.

X or Y
     If X => true, do not evaluate Y and return true.

Thus, in the expression not relayed(hostname($client_addr)) and rcpt_count > 10, the value of the rcpt_count variable will be compared with 10 only if the relayed function yielded false.

To further enhance our sample filter, you may wish to make the reject output more informative, to let the sender know what the recipient limit is.  To do so, you can use the concatenation operator . (a dot):

     set max_rcpt 10
     prog envrcpt
     do
       if not relayed(hostname($client_addr)) and rcpt_count > 10
         reject 550 5.7.1 "Too many recipients, max=" . max_rcpt
       fi
     done

When evaluating the third argument to reject, mailfromd will first convert max_rcpt to string and then concatenate both strings together, producing string Too many recipients, max=10.

Sending Rate
============

We have introduced the notion of mail sending rate in Rate Limit.  Mailfromd keeps the computed rates in the special rate database (see Databases).  Each record in this database consists of a key, for which the rate is computed, and the rate value, in form of a double precision floating point number, representing average number of messages per second sent by this key within the last sampling interval.  In the simplest case, the sender email address can be used as a key, however we recommend to use a conjunction EMAIL-SENDER_IP instead, so the actual EMAIL owner won't be blocked by actions of some spammer abusing his/her address.

Two functions are provided to control and update sending rates.  The rateok function takes three mandatory arguments:

       bool rateok(string KEY, number INTERVAL, number THRESHOLD)

The KEY meaning is described above.  The INTERVAL is the sampling interval, or the number of seconds to which the actual sending rate value is converted.  Remember that it is stored internally as a floating point number, and thus cannot be directly used in mailfromd filters, which operate only on integer numbers.  To use the rate value, it is first converted to messages per given interval, which is an integer number.  For example, the rate 0.138888 brought to 1-hour interval gives 500 (messages per hour).

When the rateok function is called, it recomputes rate record for the given KEY.  If the new rate value converted to messages per given INTERVAL is less than THRESHOLD, the function updates the database and returns True.  Otherwise it returns False and does not update the database.

This function must be required prior to use, by placing the following statement somewhere at the beginning of your script:

     require rateok

For example, the following code limits the mail sending rate for each email address-IP combination to 180 per hour. If the actual rate value exceeds this limit, the sender is returned a temporary failure response:

     require rateok

     prog envfrom
     do
       if not rateok($f . "-" . ${client_addr}, 3600, 180)
         tempfail 450 4.7.0 "Mail sending rate exceeded.  Try again later"
       fi
     done

Notice argument concatenation, used to produce the key.

It is often inconvenient to specify intervals in seconds, therefore a special interval function is provided.  It converts its argument, which is a textual string representing time interval in English, to the corresponding number of seconds.  Using this function, the function invocation would be:

          rateok($f . "-" . ${client_addr}, interval("1 hour"), 180)

The interval function is described in interval, and time intervals are discussed in time interval specification.

The rateok function begins computing the rate as soon as it has collected enough data.  By default, it needs at least four mails.  Since this may lead to a big number of false positives (i.e. overestimated rates) at the beginning of sampling interval, there is a way to specify a minimum number of samples rateok must collect before starting to actually compute rates.  This number of samples is given as the optional fourth argument to the function.  For example, the following call will always return True for the first 10 mails, no matter what the actual rate:

          rateok($f . "-" . ${client_addr}, interval("1 hour"), 180, 10)

The tbf_rate function allows to exercise more control over the mail rates.  This function implements a token bucket filter (TBF) algorithm.

The token bucket controls when the data can be transmitted based on the presence of abstract entities called tokens in a container called bucket.  Each token represents some amount of data.  The algorithm works as follows:

  * A token is added to the bucket at a constant rate of 1 token per T microseconds.

  * A bucket can hold at most M tokens.  If a token arrives when the bucket is full, that token is discarded.

  * When N items of data arrive (e.g. N mails), N tokens are removed from the bucket and the data are accepted.

  * If fewer than N tokens are available, no tokens are removed from the bucket and the data are not accepted.

This algorithm allows to keep the data traffic at a constant rate T with bursts of up to M data items.  Such bursts occur when no data was being arrived for M*T or more microseconds.

Mailfromd keeps buckets in a database tbf.  Each bucket is identified by a unique key.  The tbf_rate function is defined as follows:

      bool tbf_rate(string KEY, number N, number T, number M)

The KEY identifies the bucket to operate upon.  The rest of arguments is described above.  The tbf_rate function returns True if the algorithm allows to accept the data and False otherwise.

Depending on how the actual arguments are selected the tbf_rate function can be used to control various types of flow rates.  For example, to control mail sending rate, assign the arguments as follows: N to the number of mails and T to the control interval in microseconds:

     prog envfrom
     do
       if not tbf_rate($f . "-" . $client_addr, 1, 10000000, 20)
         tempfail 450 4.7.0 "Mail sending rate exceeded.  Try again later"
       fi
     done

The example above permits to send at most one mail each 10 seconds. The burst size is set to 20.

Another use for the tbf_rate function is to limit the total delivered mail size per given interval of time.  To do so, the function must be used in prog eom handler, because it is the only handler where the entire size of the message is known.   The N argument must contain the number of bytes in the email (or email bytes * number of recipients), and the T must be set to the number of bytes per microsecond a given user is allowed to send.  The M argument must be large enough to accommodate a couple of large emails.  E.g.:

       prog eom
       do
         if not tbf_rate("$f-$client_addr",
                         message_size(current_message()),
                         10240*1000000,  # At most 10 kb/sec
                         10*1024*1024)
           tempfail 450 4.7.0 "Data sending rate exceeded.  Try again later"
         fi
       done

See Rate limiting functions, for more information about rateok and tbf_rate functions.

Greylisting
===========

Greylisting is a simple method of defending against the spam proposed by Evan Harris.  In few words, it consists in recording the sender IP-sender email-recipient email triplet of mail transactions.  Each time the unknown triplet is seen, the corresponding message is rejected with the tempfail code.  If the mail is legitimate, this will make the originating server retry the delivery later, until the destination eventually accepts it.  If, however, the mail is a spam, it will probably never be retried, so the users will not be bothered by it.  Even if the spammer will retry the delivery, the greylisting period will give spam-detection systems, such as DNSBLs, enough time to detect and blacklist it, so by the time the destination host starts accepting emails from this triplet, it will already be blocked by other means.

You will find the detailed description of the method in The Next Step in the Spam Control War: Greylisting (http://projects.puremagic.com/greylisting/whitepaper.html), the original whitepaper by Evan Harris.

The mailfromd implementation of greylisting is based on greylist function.  The function takes two arguments: the key, identifying the greylisting triplet, and the interval.  The function looks up the key in the greylisting database.  If such a key is not found, a new entry is created for it and the function returns true.  If the key is found, greylist returns false, if it was inserted to the database more than interval seconds ago, and true otherwise. In other words, from the point of view of the  greylisting algorithm, the function returns true when the message delivery should be blocked.  Thus, the simplest implementation of the algorithm would be:

     prog envrcpt
     do
      if greylist("${client_addr}-$f-${rcpt_addr}", interval("1 hour"))
        tempfail 451 4.7.1 "You are greylisted"
      fi
     done

However, the message returned by this example, is not informative enough.  In particular, it does not tell when the message will be accepted.  To help you produce more informative messages, greylist function stores the number of seconds left to the end of the greylisting period in the global variable greylist_seconds_left, so the above example could be enhanced as follows:

     prog envrcpt
     do
       set gltime interval("1 hour")
       if greylist("${client_addr}-$f-${rcpt_addr}", gltime)
         if greylist_seconds_left = gltime
           tempfail 451 4.7.1
              "You are greylisted for %gltime seconds"
         else
           tempfail 451 4.7.1
              "Still greylisted for %greylist_seconds_left seconds"
         fi
       fi
     done

In real life you will have to avoid greylisting some messages, in particular those coming from the <> address and from the IP addresses in your relayed domain.  It can easily be done using the techniques described in previous sections and is left as an exercise to the reader.

Mailfromd provides two implementations of greylisting primitives, which differ in the information stored in the database. The one described above is called traditional.  It keeps in the database the time when the greylisting was activated for the given key, so the greylisting function uses its second argument (interval) and the current timestamp to decide whether the key is still greylisted.

The second implementation is called by the name of its inventor Con Tassios.  This implementation stores in the database the time when the greylisting period is set to expire, computed by the greylist when it is first called for the given key, using the formula current_timestamp + interval.  Subsequent calls to greylist compare the current timestamp with the one stored in the database and ignore their second argument.  This implementation is enabled by one of the following pragmas:

     #pragma greylist con-tassios

or

     #pragma greylist ct

When Con Tassios implementation is used, yet another function becomes available.  The function is_greylisted (see is_greylisted) returns True if its argument is greylisted and False otherwise. It can be used to check for the greylisting status without actually updating the database:

       if is_greylisted("${client_addr}-$f-${rcpt_addr}")
         ...
       fi

One special case is whitelisting, which is often used together with greylisting.  To implement it, mailfromd provides the function dbmap, which takes two mandatory arguments: dbmap(FILE, KEY) (it also allows an optional third argument, see dbmap, for more information on it).  The first argument is the name of the DBM file where to search for the key, the second one is the key to be searched.  Assuming you keep your whitelist database in file /var/run/whitelist.db, a more practical example will be:

     prog envrcpt
     do
       set gltime interval("1 hour")

       if not ($f = "" or relayed(hostname(${client_addr}))
              or dbmap("/var/run/whitelist.db", ${client_addr}))
         if greylist("${client_addr}-$f-${rcpt_addr}", gltime)
           if greylist_seconds_left = gltime
             tempfail 451 4.7.1
                "You are greylisted for %gltime seconds"
           else
             tempfail 451 4.7.1
                "Still greylisted for %greylist_seconds_left seconds"
           fi
         fi
       fi
     done

Local Account Verification
==========================

In your filter script you may need to verify if the given user name is served by your mail server, in other words, to verify if it represents a local account.  Notice that in this context, the word local does not necessarily mean that the account is local for the server running mailfromd, it simply means any account whose mailbox is served by the mail servers using mailfromd.

The validuser function may be used for this purpose.  It takes one argument, the user name, and returns true if this name corresponds to a local account.  To verify this, the function relies on libmuauth, a powerful authentication library shipped with GNU mailutils.  More precisely, it invokes a list of authorization functions.  Each function is responsible for looking up the user name in a particular source of information, such as system passwd database, an SQL database, etc.  The search is terminated when one of the functions finds the name in question or the list is exhausted.  In the former case, the account is local, in the latter it is not.  This concept is discussed in detail in see Authorization and Authentication Principles (GNU Mailutils Manual)).  Here we will give only some practical advices for implementing it in mailfromd filters.

The actual list of available authorization modules depends on your mailutils installation.  Usually it includes, apart from traditional UNIX passwd database, the functions for verifying PAM, RADIUS and SQL database accounts. Each of the authorization methods is configured using special configuration file statements.  For the description of the Mailutils configuration files, see Mailutils Configuration File (GNU Mailutils Manual). You can obtain the template for mailfromd configuration by running mailfromd --config-help.

For example, the following mailfromd.conf file:

     auth {
       authorization pam:system;
     }

     pam {
       service mailfromd;
     }

sets up the authorization using PAM and system passwd database.  The name of PAM service to use is mailfromd.

The function validuser is often used together with dbmap, as in the example below:

     #pragma dbprop /etc/mail/aliases.db null

     if dbmap("/etc/mail/aliases.db", localpart($rcpt_addr))
        and validuser(localpart($rcpt_addr))
       ...
     fi

For more information about dbmap function, see dbmap. For a description of dbprop pragma, see Database functions.

Databases
=========

Some mailfromd functions use DBM databases to save their persistent state data.  Each database has a unique identifier, and is assigned several pieces of information for its maintenance: the database file name and the expiration period, i.e. the time after which a record is considered expired.

To obtain the list of available databases along with their preconfigured settings, run mailfromd --show-defaults.  You will see an output similar to this:

     version:             VERSION
     script file:         /etc/mailfromd.mf
     preprocessor:        /usr/bin/m4 -s
     user:                mail
     statedir:            /var/run/mailfromd
     socket:              unix:/var/run/mailfromd/mailfrom
     pidfile:             /var/run/mailfromd/mailfromd.pid
     default syslog:          blocking
     supported databases:     gdbm, bdb
     default database type:   bdb
     optional features:   GeoIP
     greylist database:      /var/run/mailfromd/greylist.db
     greylist expiration:    86400
     tbf database:        /var/run/mailfromd/tbf.db
     tbf expiration:      86400
     rate database:      /var/run/mailfromd/rates.db
     rate expiration:    86400
     cache database:      /var/run/mailfromd/mailfromd.db
     cache positive expiration: 86400
     cache negative expiration: 43200

The text below optional features line describes the available built-in databases.  Notice that the cache database, in contrast to the rest of databases, has two expiration periods associated with it.  This is explained in the next subsection.

Database Formats
----------------

The version VERSION runs the following database types (or formats):

cache
     Cache database keeps the information about external emails, obtained using sender verification functions (see Checking Sender Address).  The key entry to this database is an email address or EMAIL:SENDER-IP string, for addresses checked using strict verification.  The data its stores for each key are:

      1. Address validity.  This field can be either success or not_found, meaning the address is confirmed to exists or it is not.

      2. The time when the entry was entered into the database.  It is used to check for expired entries.

     The cache database has two expiration periods: a positive expiration period, that is applied to  entries with the first field set to success, and a negative expiration period, applied to entries marked as not_found.

rate
     The mail sending rate data, maintained by rate function (see Rate limiting functions).  A record consists of the following fields:

     timestamp
          The time when the entry was entered into the database.

     interval
          Interval during which the rate was measured (seconds).

     count
          Number of mails sent during this interval.

tbf
     This database is maintained by tbf_rate function (see TBF). Each record represents a single bucket and consists of the following keys:

     timestamp
          Timestamp of most recent token, as a 64-bit unsigned integer (microseconds resolution).

     expirytime
          Estimated time when this bucket expires (seconds since epoch).

     tokens
          Number of tokens in the bucket (size_t).

greylist
     This database is maintained by greylist function (see Greylisting).  Each record holds only the timestamp. Its semantics depends on the greylisting implementation in use (see greylisting types).  In traditional implementation, it is the time when the entry was entered into the database.  In Con Tassios implementation, it is the time when the greylisting period expires.

Basic Database Operations
-------------------------

The mfdbtool utility is provided for performing various operations on the mailfromd database.

To list the contents of a database, use --list option. When used without any arguments it will list the cache database:

     $ mfdbtool --list
     abrakat@mail.com           success Thu Aug 24 15:28:58 2006
     baccl@EDnet.NS.CA          not_found Fri Aug 25 10:04:18 2006
     bhzxhnyl@chello.pl       not_found Fri Aug 25 10:11:57 2006
     brqp@aaanet.ru:24.1.173.165  not_found Fri Aug 25 14:16:06 2006

You can also list data for any particular key or keys.  To do so, give the keys as arguments to mfdbtool:

     $ mfdbtool --list abrakat@mail.com brqp@aaanet.ru:24.1.173.165
     abrakat@mail.com           success Thu Aug 24 15:28:58 2006
     brqp@aaanet.ru:24.1.173.165  not_found Fri Aug 25 14:16:06 2006

To list another database, give its format identifier with the --format (-H) option.  For example, to list the rate database:

     $ mfdbtool --list --format=rate
     sam@mail.net-62.12.4.3 Wed Sep  6 19:41:42 2006  139   3 0.0216 6.82e-06
     axw@rame.com-59.39.165.172 Wed Sep  6 20:26:24 2006  0  1  N/A  N/A

The --format option can be used with any database management option, described below.

Another useful operation you can do while listing rate database is the prediction of estimated time of sending, i.e. the time when the user will be able to send mail if currently his mail sending rate has exceeded the limit.  This is done using --predict option.  The option takes an argument, specifying the mail sending rate limit, e.g. (the second line is split for readability):

     $ mfdbtool --predict="180 per 1 minute"
     ed@fae.net-21.10.1.2 Wed Sep 13 03:53:40 2006  0 1 N/A N/A; free to send
     service@19.netlay.com-69.44.129.19 Wed Sep 13 15:46:07 2006 7 2
        0.286   0.0224; in 46 sec. on Wed Sep 13 15:49:00 2006

Notice, that there is no need to use --list --format=rate along with this option, although doing so is not an error.

To delete an entry from the database, use --delete option, for example: mfdbtool --delete abrakat@mail.com.  You can give any number of keys to delete in the command line.

Database Maintenance
--------------------

There are two principal operations of database management: expiration and compaction.  Expiration consists in removing expired entries from the database.  In fact, it is rarely needed, since the expired entries are removed in the process of normal mailfromd work.  Nevertheless, a special option is provided in case an explicit expiration is needed (for example, before dumping the database to another format, to avoid transferring useless information).

The command line option --expire instructs mfdbtool to delete expired entries from the specified database.  As usual, the database is specified using --format option.  If it is not given explicitly, cache is assumed.

While removing expired entries the space they occupied is marked as free, so it can be used by subsequent inserts.  The database does not shrink after expiration is finished.  To actually return the unused space to the file system you should compact your database.

This is done by running mfdbtool --compact (and, optionally, specifying the database to operate upon with --format option).  Notice, that compacting a database needs roughly as much disk space on the partition where the database resides as is currently used by the database.  Database compaction runs in three phases. First, the database is scanned and all non-expired records are stored in the memory.  Secondly, a temporary database is created in the state directory and all the cached entries are flushed into it.  This database is named after the PID of the running mfdbtool process.  Finally, the temporary database is renamed to the source database.

Both --compact and --expire can be applied to all databases by combining them with --all.  It is useful, for example, in crontab files.  For example, I have the following monthly job in my crontab:

     0 1 1 * * /usr/bin/mfdbtool --compact --all

Testing Filter Scripts
======================

It is important to check your filter script before actually starting to use it.  There are several ways to do so.

To test the syntax of your filter script, use the --lint option.  It will cause mailfromd to exit immediately after attempting to compile the script file.  If the compilation succeeds, the program will exit with code 0.  Otherwise, it will exit with error code 78 (configuration error).  In the latter case, mailfromd will also print a diagnostic message, describing the error along with the exact location where the error was diagnosed, for example:

     mailfromd: /etc/mailfromd.mf:39: syntax error, unexpected reject

The error location is indicated by the name of the file and the number of the line when the error occurred.  By using the --location-column option you instruct mailfromd to also print the column number.  E.g. with this option the above error message may look like:

     mailfromd: /etc/mailfromd.mf:39.12 syntax error, unexpected reject

Here, 39 is the line and 12 is the column number.

For complex scripts you may wish to obtain a listing of variables used in the script.  This can be achieved using --xref command line option:

The output it produces consists of four columns:

Variable name

Data type
     Either number or string.

Offset in data segment
     Measured in words.

References
     A comma-separated list of locations where the variable was referenced.  Each location is represented as FILE:LINE. If several locations pertain to the same FILE, the file name is listed only once.

Here is an example of the cross-reference output:

     $ mailfromd --xref
     Cross-references:
     -----------------
     cache_used               number 5   /etc/mailfromd.mf:48
     clamav_virus_name        string 9   /etc/mailfromd.mf:240,240
     db                       string 15  /etc/mailfromd.mf:135,194,215
     dns_record_ttl           number 16  /etc/mailfromd.mf:136,172,173
     ehlo_domain              string 11
     gltime                   number 13  /etc/mailfromd.mf:37,219,220,222,223
     greylist_seconds_left    number 1   /etc/mailfromd.mf:220,226,227
     last_poll_host           string 2

If the script passes syntax check, the next step is often to test if it works as you expect it to.  This is done with --test (-t) command line option.  This option runs the envfrom handler (or another one, see below) and prints the result of its execution.

When running your script in test mode, you will need to supply the values of Sendmail macros it needs.  You do this by placing the necessary assignments in the command line.  For example, this is how to supply initial values for f and client_addr macros:

     $ mailfromd --test f=gray@gnu.org client_addr=127.0.0.1

You may also need to alter initial values of some global variables your script uses.  To do so, use -v (--variable) command line option.  This option takes a single argument consisting of the variable name and its initial value, separated by an equals sign.  For example, here is how to change the value of ehlo_domain global variable:

     $ mailfromd -v ehlo_domain=mydomain.org

The --test option is often useful in conjunction with options --debug, --trace and --transcript (see Logging and Debugging.  The following example shows what the author got while debugging the filter script described in Filter Script Example:

     $ mailfromd --test --debug=50 f=gray@gnu.org client_addr=127.0.0.1
     MX 20 mx20.gnu.org
     MX 10 mx10.gnu.org
     MX 10 mx10.gnu.org
     MX 20 mx20.gnu.org
     getting cache info for gray@gnu.org
     found status: success (0), time: Thu Sep 14 14:54:41 2006
     getting rate info for gray@gnu.org-127.0.0.1
     found time: 1158245710, interval: 29, count: 5, rate: 0.172414
     rate for gray@gnu.org-127.0.0.1 is 0.162162
     updating gray@gnu.org-127.0.0.1 rates
     SET REPLY 450 4.7.0 Mail sending rate exceeded.  Try again later
     State envfrom: tempfail

To test any handler, other than envfrom, give its name as the argument to --test option.  Since this argument is optional, it is important that it be given immediately after the option, without any intervening white space, for example mailfromd --test=helo, or mailfromd -thelo.

This method allows to test one handler at a time.  To test the script as a whole, use mtasim utility.  When started it enters interactive mode, similar to that of sendmail -bs, where it expects SMTP commands on its standard input and sends answers to the standard output.  The --port=auto command line option instructs it to start mailfromd and to create a unique socket for communication with it.  For the detailed description of the program and the ways to use it, see mtasim.

Run Mode
========

Mailfromd provides a special option that allows to run arbitrary MFL scripts.  This is an experimental feature, intended for future use of MFL as a scripting language.

When given the --run command line option, mailfromd loads the script given in its command line and executes a function called main.

The function main must be declared as:

     func main(...) returns number

Mailfromd passes all command line arguments that follow the script name as arguments to that function.  When the function returns, its return value is used by mailfromd as exit code.

As an example, suppose the file script.mf contains the following:

     func main (...)
       returns number
     do
       loop for number i 1,
            while i <= $#,
            set i i + 1
       do
         echo "arg %i=" . $(i)
       done
     done

This function prints all its arguments (see variadic functions, for a detailed description of functions with variable number of arguments).  Now running:

     $ mailfromd --run script.mf 1 file dest

displays the following:

     arg 1=1
     arg 2=file
     arg 3=dest

Note, that MFL does not have a direct equivalent of shell's $0 argument.  If your function needs to know the name of the script that is being executed, use __file__ built-in constant instead (see __file__.

You may name your start function with any name other than the default main.  In this case, give its name as an argument to the --run option.  This argument is optional, therefore it must be separated from the option by an equals sign (with no whitespace from either side).  For example, given the command line below, mailfromd loads the file script.mf and execute the function named start:

     $ mailfromd --run=start script.mf

The Top of a Script File
------------------------

The --run option makes it possible to use mailfromd scripts as standalone programs.  The traditional way to do so was to set the executable bit on the script file and to begin the script with the interpreter selector, i.e. the characters #! followed by the name of the mailfromd executable, e.g.:

     #! /usr/sbin/mailfromd --run

This would cause the shell to invoke mailfromd with the command line constructed from the --run option, the name of the invoked script file itself, and any actual arguments from the invocation.  Once invoked, mailfromd would treat the initial #! line as a usual single-line comment (see Comments).

However, the interpretation of the #! by shells has various deficiencies, which depend on the actual shell being used.  For example, some shells pass any characters following the whitespace after the interpreter name as a single argument, some others silently truncate the command line after some number of characters, etc.  This often make it impossible to pass additional arguments to mailfromd.  For example, a script which begins with the following line would most probably fail to be executed properly:

     #! /usr/sbin/mailfromd --no-config --run

To compensate for these deficiencies and to allow for more complex invocation sequences, mailfromd handles initial # in a special way.  If the first line of a source file begins with #!/ or #! / (with a single space between ! and /), it is treated as a start of a multi-line comment, which is closed by the two characters !# on a line by themselves.

Thus, the correct way to begin a mailfromd script is:

     #! /usr/sbin/mailfromd --run
     !#

Using this feature, you can start the mailfromd with arbitrary shell code, provided it ends with an exec statement invoking the interpreter itself.  For example:

     #!/bin/sh
     exec /usr/sbin/mailfromd --no-config --run $0 $@
     !#

     func main(...)
       returns number
     do
       /* actual mfl code goes here */
     done

Note the use of $0 and $@ to pass the actual script file name and command line arguments to mailfromd.

Parsing Command Line Arguments
------------------------------

A special function is provided to break (parse) options in command lines, and to check for legal options.  It uses the GNU getopt routines (see getopt (The GNU C Library Reference Manual)).

 -- Built-in Function: string getopt (number ARGC,
     pointer ARGV, ...)
     The getopt function parses the command line arguments, as supplied by ARGC and ARGV.  The ARGC argument is the argument count, and ARGV is an opaque data structure, representing the array of arguments (When MFL has array data type, the second argument will change to array of strings.).  The operator vaptr (see vaptr) is provided to initialize this argument.

     An argument that starts with - (and is not exactly - or --), is an option element.  An argument that starts with a - is called short or traditional option.  The characters of this element, except for the initial - are option characters.  Each option character represents a separate option.  An argument that starts with -- is called long or GNU option.  The characters of this element, except for the initial -- form the option name.

     Options may have arguments.  The argument to a short option is supplied immediately after the option character, or as the next word in command line.  E.g., if option -f takes a mandatory argument, then it may be given either as -farg or as -f arg.  The argument to a long option is either given immediately after it and separated from the option name by an equals sign (as --file=arg), or is given as the next word in the command line (e.g. --file arg).

     If the option argument is optional, i.e. it may not necessarily be given, then only the first form is allowed (i.e. either -farg or --file=arg.

     The -- command line argument ends the option list.  Any arguments following it are not considered options, even if they begin with a dash.

     If getopt is called repeatedly, it returns successively each of the option characters from each of the option elements (for short options) and each option name (for long options).  In this case, the actual arguments are supplied only to the first invocation. Subsequent calls must be given two nulls as arguments.  Such invocation instructs getopt to use the values saved on the previous invocation.

     When the function finds another option, it returns its character or name updating the external variable optind (see below) so that the next call to getopt can resume the scan with the following option.

     When there are no more options left, or a -- argument is encountered, getopt returns an empty string.  Then optind gives the index in ARGV of the first element that is not an option.

     The legitimate options and their characteristics are supplied in additional arguments to getopt.  Each such argument is a string consisting of two parts, separated by a vertical bar (|).  Any one of these parts is optional, but at least one of them must be present.  The first part specifies short option character.  If it is followed by a colon, this character takes mandatory argument.  If it is followed by two colons, this character takes an optional argument. If only the first part is present, the | separator may be omitted.  Examples:

     "c"
     "c|"
          Short option -c.

     "f:"
     "f:|"
          Short option -f, taking a mandatory argument.

     "f::"
     "f::|"
          Short option -f, taking an optional argument.

     If the vertical bar is present and is followed by any characters, these characters specify the name of a long option, synonymous to the short one, specified by the first part.  Any mandatory or optional arguments to the short option remain mandatory or optional for the corresponding long option.  Examples:

     "f:|file"
          Short option -f, or long option --file, requiring an argument.

     "f::|file"
          Short option -f, or long option --file, taking an optional argument.

     In any of the above cases, if this option appears in the command line, getopt returns its short option character.

     To define a long option without a short equivalent, begin it with a bar, e.g.:

     "|help"

     If this option is to take an argument, this is specified using the mechanism described above, except that the short option character is replaced with a minus sign.  For example:

     "-:|output"
          Long option --output, which takes a mandatory argument.

     "-::|output"
          Long option --output, which takes an optional argument.

     If an option is returned that has an argument in the command line, getopt stores this argument in the variable optarg.

     After each invocation, getopt sets the variable optind to the index of the next ARGV element to be parsed.  Thus, when the list of options is exhausted and the function returned an empty string, optind contains the index of the the first element that is not an option.

     When getopt encounters an option that is not described in its arguments or if it detects a missing option argument it prints an error message using mailfromd logging facilities, stores the offending option in the variable optopt, and returns ?.

     If printing error message is not desired (e.g. the application is going to take care of error messaging), it can be disabled by setting the variable opterr to 0.

     The third argument to getopt, called controlling argument, may be used to control the behavior of the function.  If it is a colon, it disables printing the error message for unrecognized options and missing option arguments (as setting opterr to 0 does).  In this case getopt returns :, instead of ? to indicate missing option argument.

     If the controlling argument is a plus sign, or the environment variable POSIXLY_CORRECT is set, then option processing stops as soon as a non-option argument is encountered.  By default, if options and non optional arguments are intermixed in ARGV, getopt permutes them so that the options go first, followed by non-optional arguments.

     If the controlling argument is -, then each non-option element in ARGV is handled as if it were the argument of an option with character code 1 ("\001", in MFL notation.  This can used by programs that are written to expect options and other ARGV-elements in any order and that care about the ordering of the two.

     Any other value of the controlling argument is handled as an option definition.

A special language construct is provided to supply the second argument (ARGV) to getopt and similar functions:

     vaptr(PARAM)

where PARAM is a positional parameter, from which to start the array of ARGV.  For example:

     func main(...)
       returns number
     do
       set rc getopt($#, vaptr($1), "|help")
       ...

Here, vaptr($1) constructs the ARGV array from all the arguments, supplied to the function main.

To illustrate the use of getopt function, let's suppose you write a script that takes the following options:

-f FILE
--file=FILE

--output[=DIR]

--help

Then, the corresponding getopt invocation will be:

     func main(...)
       returns number
     do
       loop for string rc getopt($#, vaptr($1),
                                 "f:|file", "-::|output", "h|help"),
            while rc != "",
            set rc getopt(0, 0)
       do
         switch rc
         do
           case "f":
             set file optarg
           case "output"
             set output 1
             set output_dir optarg
           case "h"
             help()
           default:
             return 1
         done
         ...

Logging and Debugging
=====================

Depending on its operation mode, mailfromd tries to guess whether it is appropriate to print its diagnostics and informational messages on standard error or to send them to syslog.  Standard error is assumed if the program is run with one of the following command line options:

  * --test (see Testing Filter Scripts)

  * --run (see Run Mode)

  * --lint (see Testing Filter Scripts)

  * --dump-code (see Logging and Debugging Options)

  * --dump-grammar-trace (see Logging and Debugging Options)

  * --dump-lex-trace (see Logging and Debugging Options)

  * --dump-macros (see Logging and Debugging Options)

  * --dump-tree (see Logging and Debugging Options)

  * --xref or --dump-xref) (see Testing Filter Scripts)

If none of these are used, mailfromd switches to syslog as soon as it finishes its startup.  There are two ways to communicate with the syslogd daemon: using the syslog function from the system libc library, which is a blocking implementation in most cases, or via internal, asynchronous, syslog implementation.  Whether the latter is compiled in and which of the implementation is used by default is determined while compiling the package, as described in Using non-blocking syslog.

The --logger command line option allows you to manually select the diagnostic channel:

--logger=stderr
     Log everything to the standard error.

--logger=syslog
     Log to syslog.

--logger=syslog:async
     Log to syslog using the asynchronous syslog implementation.

Another way to select the diagnostic channel is by using the logger statement in the configuration file.  The statement takes the same argument as its command line counterpart.

The rest of details regarding diagnostic output are controlled by the logging configuration statement.

The default syslog facility is mail; it can be changed using the --log-facility command line option or facility statement.  Argument in both cases is a valid facility name, i.e. one of: user, daemon, auth, authpriv, mail, and local0 through local7.  The argument can be given in upper, lower or mixed cases, and it can be prefixed with log_:

Another syslog-related parameter that can be configured is the tag, which identifies mailfromd messages.  The default tag is the program name.  It is changed by the --log-tag (-L command line option and the tag logging statement.

The following example configures both the syslog facility and tag:

     logging {
       facility local7;
       tag "mfd";
     }

As any other UNIX utility, mailfromd is very quiet unless it has something important to communicate, such as, e.g. an error condition. A set of command line options is provided for controlling the verbosity of its output.

The --trace option enables tracing Sendmail actions executed during message verifications.  When this option is given, any accept, discard, continue, etc. triggered during execution of your filter program will leave their traces in the log file.  Here is an example of how it looks like (syslog time stamp, tag and PID removed for readability):

     k8DHxvO9030656: /etc/mailfromd.mf:45: reject 550 5.1.1 Sender validity
     not confirmed

This shows that while verifying the message with ID k8DHxvO9030656 the reject action was executed by filter script /etc/mailfromd.mf at line 45.

The use of message ID in the log deserves a special notice.  The program will always identify its log messages with the Message-Id, when it is available.  Your responsibility as an administrator is to make sure it is available by configuring your MTA to export the macro i to mailfromd. The rule of thumb is: make i available to the very first handler mailfromd executes.  It is not necessary to export it to the rest of the handlers, since mailfromd will cache it.  For example, if your filter script contains envfrom and envrcpt handlers, export i for envfrom. The exact instructions on how to ensure it depend on the MTA you use.  For Sendmail, refer to Sendmail. For MeTA1, see MeTA1, and pmult-macros.  For Postfix, see Postfix.

To push log verbosity further, use the debug configuration statement (see conf-debug) or its command line equivalent, --debug (-d, see --debug).  Its argument is a debugging level, whose syntax is described in http://mailutils.org/wiki/Debug_level.

The debugging output is controlled by a set of levels, each of which can be set independently of others.  Each debug level consists of a category name, which identifies the part of package for which additional debugging is desired, and a level number, which indicates how verbose should its output be.

Valid debug levels are:

error
     Displays error conditions which are normally not reported, but passed to the caller layers for handling.

trace0 through trace9
     Ten levels of verbosity, trace0 producing less output, trace9 producing the maximum amount of output.

prot
     Displays network protocol interaction, where applicable.

The overall debugging level is specified as a list of individual levels, delimited with semicolons.  Each individual level can be specified as one of:

!CATEGORY
     Disables all levels for the specified category.

CATEGORY
     Enables all levels for the specified category.

CATEGORY.LEVEL
     For this category, enables all levels from error to LEVEL, inclusive.

CATEGORY.=LEVEL
     Enables only the given LEVEL in this CATEGORY.

CATEGORY.!LEVEL
     Disables all levels from error to LEVEL, inclusive, in this CATEGORY.

CATEGORY.!=LEVEL
     Disables only the given LEVEL in this CATEGORY.

CATEGORY.LEVELA-LEVELB
     Enables all levels in the range from LEVELA to LEVELB, inclusive.

CATEGORY.!LEVELA-LEVELB
     Disables all levels in the range from LEVELA to LEVELB, inclusive.

Additionally, a comma-separated list of level specifications is allowed after the dot.  For example, the following specification:

     acl.prot,!=trace9,!trace2

enables in category acl all levels, except trace9, trace0, trace1, and trace2.

Implementation and applicability of each level of debugging differs between various categories.  Categories built-in to mailutils are described in http://mailutils.org/wiki/Debug_level.  Mailfromd introduces the following additional categories:

db

     trace0
          Detailed debugging info about expiration and compaction.

     trace5
          List records being removed.

dns

     trace8
          Verbose information about attempted DNS queries and their results.

     trace9
          Enables libadns internal debugging.

srvman

     trace0
          Additional information about normal conditions, such as subprocess exiting successfully or a remote party being allowed access by ACL.

     trace1
          Detailed transcript of server manager actions: startup, shutdown, subprocess cleanups, etc.

     trace3
          Additional info about fd sets.

     trace4
          Individual subserver status information.

     trace5
          Subprocess registration.

pmult

     trace1
          Verbosely list incoming connections, functions being executed and erroneous conditions: missing headers in SMFIR_CHGHEADER, undefined macros, etc.

     trace2
          List milter requests being processed.

     trace7
          List SMTP body content in SMFIR_REPLBODY requests.

     error
          Verbosely list mild errors encountered: bad recipient addresses, etc.

callout

     trace0
          Verification session transcript.

     trace1
          MX servers checks.

     trace5
          List emails being checked.

     trace9
          Additional info.

main

     trace5
          Info about hostnames in relayed domain list

engine
     Debugging of the virtual engine.

     trace5
          Message modification lists.

     trace6
          Debug message modification operations and Sendmail macros registered.

     trace7
          List SMTP stages (xxfi_* calls).

     trace9
          Cleanup calls.

pp
     Preprocessor.

     trace1
          Show command line of the preprocessor being run.

prog

     trace8
          Stack operations

     trace9
          Debug exception state save/restore operations.

spf

     error
          Mild errors.

     trace0
          List calls to spf_eval_record, spf_test_record, spf_check_host_internal, etc.

     trace1
          General debug info.

     trace6
          Explicitly list A records obtained when processing the a SPF mechanism.

Categories starting with bi_ debug built-in modules:

bi_db
     Database functions.

     trace5
          List database look-ups.

     trace6
          Trace operations on the greylisting database.

bi_sa
     SpamAssassin and ClamAV API.

     trace1
          Report the findings of the clamav function.

     trace9
          Trace payload in interactions with spamd.

bi_io
     I/O functions.

     trace1
          Debug the following functions: open, spawn, write.

     trace2
          Report stderr redirection.

     trace3
          Report external commands being run.

bi_mbox
     Mailbox functions.

     trace1
          Report opened mailboxes.

bi_other
     Other built-ins.

     trace1
          Report results of checks for existence of usernames.

For example, the following invocation enables levels up to trace2 in category engine, all levels in category savsrv and levels up to trace0 in category srvman:

     $ mailfromd --debug='engine.trace2;savsrv;srvman.trace0'

You need to have sufficient knowledge about mailfromd internal structure to use this form of the --debug option.

To control the execution of the sender verification functions (see SMTP Callout functions), you may use --transcript (-X) command line option which enables transcripts of SMTP sessions in the logs.  Here is an example of the output produced running mailfromd --transcript:

     k8DHxlCa001774: RECV: 220 spf-jail1.us4.outblaze.com ESMTP Postfix
     k8DHxlCa001774: SEND: HELO mail.gnu.org.ua
     k8DHxlCa001774: RECV: 250 spf-jail1.us4.outblaze.com
     k8DHxlCa001774: SEND: MAIL FROM: <>
     k8DHxlCa001774: RECV: 250 Ok
     k8DHxlCa001774: SEND: RCPT TO: <t1Kmx17Q@malaysia.net>
     k8DHxlCa001774: RECV: 550 <>: No thank you rejected: Account
      Unavailable: Possible Forgery
     k8DHxlCa001774: poll exited with status: not_found; sent
      "RCPT TO: <t1Kmx17Q@malaysia.net>", got "550 <>: No thank you
      rejected: Account Unavailable: Possible Forgery"
     k8DHxlCa001774: SEND: QUIT

Runtime Errors
==============

A runtime error is a special condition encountered during execution of the filter program, that makes further execution of the program impossible.  There are two kinds of runtime errors: fatal errors, and uncaught exceptions.  Whenever a runtime error occurs, mailfromd writes into the log file the following message:

     RUNTIME ERROR near FILE:LINE: TEXT

where FILE:LINE indicates approximate source file location where the error occurred and TEXT gives the textual description of the error.

Fatal runtime errors
--------------------

Fatal runtime errors are caused by a condition that is impossible to fix at run time.  For version VERSION these are:

Not enough memory
     There is not enough memory for the execution of the program.  Try to make more memory available for mailfromd or to reduce its memory requirements by rewriting your filter script.

Out of stack space; increase #pragma stacksize
Heap overrun; increase #pragma stacksize
memory chunk too big to fit into heap
     These errors are reported when there is not enough space left on stack to perform the requested operation, and the attempt to resize the stack has failed.  Usually mailfromd expands the stack when the need arises (see automatic stack resizing).  This runtime error indicates that there were no more memory available for stack expansion.  Try to make more memory available for mailfromd or to reduce its memory requirements by rewriting your filter script.

Stack underflow
     Program attempted to pop a value off the stack but the stack was already empty.  This indicates an internal error in the MFL compiler or mailfromd runtime engine.  If you ever encounter this error, please report it to bug-mailfromd@gnu.org.ua.  Include the log fragment (about 10-15 lines before and after this log message) and your filter script.  See Reporting Bugs, for more information about bug reporting.

pc out of range
     The program counter is out of allowed range.  This is a severe error, indicating an internal inconsistency in mailfromd runtime engine.  If you encounter it, please report it to bug-mailfromd@gnu.org.ua.  Include the log fragment (about 10-15 lines before and after this log message) and your filter script. See Reporting Bugs, for more information about how to report a bug.

Programmatic runtime errors
---------------------------

These indicate a programmatic error in your filter script, which the MFL compiler was unable to discover at compilation stage:

Invalid exception number: N
     The throw statement used a not existent exception number N. Fix the statement and restart mailfromd.  See throw, for the information about throw statement and see Exceptions, for the list of available exception codes.

No previous regular expression
     You have used a back-reference (see Back references), where there is no previous regular expression to refer to.  Fix this line in your code and restart the program.

Invalid back-reference number
     You have used a back-reference (see Back references), with a number greater than the number of available groups in the previous regular expression.  For example:

            if $f matches "(.*)@gnu.org"
              # Wrong: there is only one group in the regexp above!
              set x \2
            ...

     Fix your code and restart the daemon.

Uncaught exceptions
-------------------

Another kind of runtime errors are uncaught exceptions, i.e. exceptional conditions for which no handler was installed (see Exceptions, for information on exceptions and on how to handle them).  These errors mean that the programmer (i.e. you), made no provision for some specific condition.  For example, consider the following code:

     prog envfrom
     do
       if $f mx matches "yahoo.com"
         foo()
       fi
     done

It is syntactically correct, but it overlooks the fact that mx matches may generate e_temp_failure exception, if the underlying DNS query has timed out (see Special comparisons).  If this happens, mailfromd has no instructions on what to do next and reports an error.  This can easily be fixed using a catch statement, e.g.:

     prog envfrom
     do
       # Catch DNS errors
       catch e_temp_failure or e_failure
       do
         tempfail 451 4.1.1 "MX verification failed"
       done

       if $f mx matches "yahoo.com"
         foo()
       fi
     done

Another common case are undefined Sendmail macros.  In this case the e_macroundef exception is generated:

     RUNTIME ERROR near foo.c:34: Macro not defined: {client_adr}

These can be caused either by misspelling the macro name (as in the example message above) or by failing to export the required name in Sendmail milter configuration (see exporting macros).  This error should be fixed either in your source code or in sendmail.cf file, but if you wish to provide a special handling for it, you can use the following catch statement:

     catch e_macroundef
     do
       ...
     done

Sometimes the location indicated with the runtime error message is not enough to trace the origin of the error.  For example, an error can be generated explicitly with throw statement (see throw):

     RUNTIME ERROR near match_cidr.mf:30: invalid CIDR (text)

If you look in module match_cidr.mf, you will see the following code (line numbers added for reference):

     23 func match_cidr(string ipstr, string cidr) returns number
     24 do
     25   number netmask
     26
     27   if cidr matches '^(([0-9]{1,3}\.){3}[0-9]{1,3})/([0-9][0-9]?)'
     28     return inet_aton(ipstr) & len_to_netmask(\3) = inet_aton(\1)
     29   else
     30     throw invcidr "invalid CIDR (%cidr)"
     31   fi
     32   return 0
     33 done

Now, it is obvious that the value of cidr argument to match_cidr was wrong, but how to find the caller that passed the wrong value to it?  The special command line option --stack-trace is provided for this.  This option enables dumping stack traces when a fatal error occurs.  The traces contain information about function calls.  Continuing our example, using the --stack-trace option you will see the following diagnostics:

     RUNTIME ERROR near match_cidr.mf:30: invalid CIDR (127%)
     mailfromd: Stack trace:
     mailfromd: 0077: match_cidr.mf:30: match_cidr
     mailfromd: 0096: test.mf:13: bar
     mailfromd: 0110: mailfromd.mf:18: foo
     mailfromd: Stack trace finishes
     mailfromd: Execution of the configuration program was not finished

Each trace line describes one stack frame.  The lines appear in the order of most recently called to least recently called.  Each frame consists of:

 1. Value of the program counter at the time of its execution;

 2. Source code location, if available;

 3. Name of the function called.

Thus, the example above can be read as: ``the function match_cidr was called by the function bar in file test.mf at line 13.  This function was called from the function bar, in file test.mf at line 13.  In its turn, bar was called by the function foo, in file mailfromd.mf at line 18''.

Examining caller functions will help you localize the source of the error and fix it.

You can also request a stack trace any place in your code, by calling the stack_trace function.  This can be useful for debugging, or in your catch statements.

Notes and Cautions
==================

This section discusses some potential culprits in the MFL.

It is important to execute special caution when writing format strings for sprintf (see String formatting) and strftime (see strftime) functions.  They use % as a character introducing conversion specifiers, while the same character is used to expand a MFL variable within a string.  To prevent this misinterpretation, always enclose format specification in single quotes (see singe-vs-double).  To illustrate this, let's consider the following example:

     echo sprintf ("Mail from %s", $f)

If a variable s is not declared, this line will produce the Variable s is not defined error message, which will allow you to identify and fix the bug.  The situation is considerably worse if s is declared.  In that case you will see no warning message, as the statement is perfectly valid, but at the run-time the variable s will be interpreted within the format string, and its value will replace %s.  To prevent this from happening, single quotes must be used:

     echo sprintf ('Mail from %s', $f)

This does not limit the functionality, since there is no need to fall back to variable interpretation in format strings.

Yet another dangerous feature of the language is the way to refer to variable and constant names within literal strings.  To expand a variable or a constant the same notation is used (see Variables, and see Constants).  Now, lets consider the following code:

     const x 2
     string x "X"

     prog envfrom
     do
       echo "X is %x"
     done

Does %x in echo refers to the variable or to the constant?  The correct answer is to the variable.  When executed, this code will print X is X.

As of version VERSION, mailfromd will always print a diagnostic message whenever it stumbles upon a variable having the same name as a previously defined constant or vice versa.  The resolution of such name clashes is described in detail in see variable--constant shadowing.

Future versions of the program may provide a non-ambiguous way of referring to variables and constants from literal strings.

Mail Filtering Language
***********************

The mail filtering language, or MFL, is a special language designed for writing filter scripts.  It has a simple syntax, similar to that of Bourne shell.  In contrast to the most existing programming languages, MFL does not have any special terminating or separating characters (like, e.g. newlines and semicolons in shell) (There are two noteworthy exceptions: require and from ... import statements, which must be terminated with a period.  See import.).  All syntactical entities are separated by any amount of white-space characters (i.e. spaces, tabulations or newlines).

The following sections describe MFL syntax in detail.

Comments
========

Two types of comments are allowed: C-style, enclosed between /* and */, and shell-style, starting with # character and extending up to the end of line:

     /* This is
        a comment. */
     # And this too.

There are, however, several special cases, where the characters following # are not ignored.

If the first line begins with #!/ or #! /, this is treated as a start of a multi-line comment, which is closed by the characters !# on a line by themselves.  This feature allows for writing sophisticated scripts.  See top-block, for a detailed description.

If # is followed by word include (with optional whitespace between them), this statement requires inclusion of the specified file, as in C.  There are two forms of the #include statement:

 1. #include <FILE>

 2. #include "FILE"

The quotes around FILE in the second form quotes are optional.

Both forms are equivalent if FILE is an absolute file name. Otherwise, the first form will look for FILE in the include search path.  The second one will look for it in the current working directory first, and, if not found there, in the include search path.

The default include search path is:

 1. PREFIX/share/mailfromd/VERSION/include

 2. PREFIX/share/mailfromd/include

 3. /usr/share/mailfromd/include

 4. /usr/local/share/mailfromd/include

     Where PREFIX is the installation prefix.

New directories can be appended in front of it using -I (--include) command line option, or include-path configuration statement (see include-path).

For example, invoking

     $ mailfromd -I/var/mailfromd -I/com/mailfromd

creates the following include search path

 1. /var/mailfromd

 2. /com/mailfromd

 3. PREFIX/share/mailfromd/VERSION/include

 4. PREFIX/share/mailfromd/include

 5. /usr/share/mailfromd/include

 6. /usr/local/share/mailfromd/include

Along with #include, there is also a special form #include_once, that has the same syntax:

     #include_once <FILE>
     #include_once "FILE"

This form works exactly as #include, except that, if the FILE has already been included, it will not be included again.  As the name suggests, it will be included only once.

This form should be used to prevent re-inclusions of a code, which can cause problems due to function redefinitions, variable reassignments etc.

A line in the form

     #line NUMBER "IDENTIFIER"

causes the MFL compiler to believe, for purposes of error diagnostics, that the line number of the next source line is given by NUMBER and the current input file is named by IDENTIFIER. If the identifier is absent, the remembered file name does not change.

Pragmatic comments
==================

If # is immediately followed by word pragma (with optional whitespace between them), such a construct introduces a pragmatic comment, i.e. an instruction that controls some configuration setting.

The available pragma types are described in the following subsections.

Pragma prereq
-------------

The #pragma prereq statement ensures that the correct mailfromd version is used to compile the source file it appears in.  It takes version number as its arguments and produces a compilation error if the actual mailfromd version number is earlier than that.  For example, the following statement:

     #pragma prereq 7.0.94

results in error if compiled with mailfromd version 7.0.93 or prior.

Pragma stacksize
----------------

The stacksize pragma sets the initial size of the run-time stack and may also define the policy of its growing, in case it becomes full.  The default stack size is STACK_SIZE words.  You may need to increase this number if your configuration program uses recursive functions or does an excessive amount of string manipulations.

 -- pragma: stacksize size [incr [max]]
     Sets stack size to SIZE units.  Optional INCR and MAX define stack growth policy (see below).  The default units are words.  The following example sets the stack size to 7168 words:

          #pragma stacksize 7168

     The SIZE may end with a unit size suffix:

     Table: Unit Size Suffix

     Suffix   Meaning
     k   Kiloword, i.e. 1024 words
     m   Megawords, i.e. 1048576 words
     g   Gigawords,
     t   Terawords (ouch!)

     File suffixes are case-insensitive, so the following two pragmas are equivalent and set the stack size to 7*1048576 = 7340032 words:

          #pragma stacksize 7m
          #pragma stacksize 7M

     When the MFL engine notices that there is no more stack space available, it attempts to expand the stack.  If this attempt succeeds, the operation continues.  Otherwise, a runtime error is reported and the execution of the filter stops.

     The optional INCR argument to #pragma stacksize defines growth policy for the stack.  Two growth policies are implemented: fixed increment policy, which expands stack in a fixed number of expansion chunks, and exponential growth policy, which duplicates the stack size until it is able to accommodate the needed number of words.  The fixed increment policy is the default.  The default chunk size is STACK_INCR words.

     If INCR is the word twice, the duplicate policy is selected.  Otherwise INCR must be a positive number optionally suffixed with a size suffix (see above).  This indicates the expansion chunk size for the fixed increment policy.

     The following example sets initial stack size to 10240, and expansion chunk size to 2048 words:

          #pragma stacksize 10M 2K

     The pragma below enables exponential stack growth policy:

          #pragma stacksize 10240 twice

     In this case, when the run-time evaluator hits the stack size limit, it expands the stack to twice the size it had before.  So, in the example above, the stack will be sequentially expanded to the following sizes: 20480, 40960, 81920, 163840, etc.

     The optional MAX argument defines the maximum size of the stack.  If stack grows beyond this limit, the execution of the script will be aborted.

If you are concerned about the execution time of your script, you may wish to avoid stack reallocations.  To help you find out the optimal stack size, each time the stack is expanded, mailfromd issues a warning in its log file, which looks like this:

     warning: stack segment expanded, new size=8192

You can use these messages to adjust your stack size configuration settings.

Pragma regex
------------

The #pragma regex, controls compilation of regular expressions.  You can use any number of such pragma directives in your mailfromd.mf.  The scope of #pragma regex extends to the next occurrence of this directive or to the end of the script file, whichever occurs first.

 -- pragma: regex [push|pop] flags
     The optional PUSH|POP parameter is one of the words push or pop and is discussed in detail below.  The FLAGS parameter is a whitespace-separated list of regex flags.  Each regex-flag is a word specifying some regex feature.  It can be preceded by + to enable this feature (this is the default), by - to disable it or by = to reset regex flags to its value.  Valid regex-flags are:

     extended
          Use POSIX Extended Regular Expression syntax when interpreting regex.  If not set, POSIX Basic Regular Expression syntax is used.

     icase
          Do not differentiate case.  Subsequent regex searches will be case insensitive.

     newline
          Match-any-character operators don't match a newline.

          A non-matching list ([^...]) not containing a newline does not match a newline.

          Match-beginning-of-line operator (^) matches the empty string immediately after a newline.

          Match-end-of-line operator ($) matches the empty string immediately before a newline.

     For example, the following pragma enables POSIX extended, case insensitive matching (a good thing to start your mailfromd.mf with):

          #pragma regex +extended +icase

Optional modifiers push and pop can be used to maintain a stack of regex flags.  The statement

     #pragma regex push [FLAGS]

saves current regex flags on stack and then optionally modifies them as requested by FLAGS.

The statement

     #pragma regex pop [FLAGS]

does the opposite: restores the current regex flags from the top of stack and applies FLAGS to it.

This statement is useful in module and include files to avoid disturbing user regex settings.  E.g.:

     #pragma regex push +extended +icase
      .
      .
      .
     #pragma regex pop

Pragma dbprop
-------------

 -- pragma: dbprop pattern prop ...
     This pragma configures properties for a DBM database. See Database functions, for its detailed description.

Pragma greylist
---------------

 -- pragma: greylist type
     Selects the greylisting implementation to use.  Allowed values for TYPE are:

     traditional
     gray
          Use the traditional greylisting implementation.  This is the default.

     con-tassios
     ct
          Use Con Tassios greylisting implementation.

     See greylisting types, for a detailed description of these greylisting implementations.

Notice, that this pragma can be used only once.  A second use of this pragma would constitute an error, because you cannot use both greylisting implementations in the same program.

Pragma miltermacros
-------------------

 -- pragma: miltermacros handler macro ...
     Declare that the Milter stage HANDLER uses MTA macro listed as the rest of arguments.  The HANDLER must be a valid handler name (see Handlers).

The mailfromd parser collects the names of the macros referred to by a $NAME construct within a handler (see Sendmail Macros) and declares them automatically for corresponding handlers.  It is, however, unable to track macros used in functions called from handler as well as those referred to via getmacro and macro_defined functions.  Such macros should be declared using #pragma miltermacros.

During initial negotiation with the MTA, mailfromd will ask it to export the macro names declared automatically or by using the #pragma miltermacros.  The MTA is free to honor or to ignore this request.  In particular, Sendmail versions prior to 8.14.0 and Postfix versions prior to 2.5 do not support this feature.  If you use one of these, you will need to export the needed macros explicitly in the MTA configuration.  For more details, refer to the section in MTA Configuration corresponding to your MTA type.

Pragma provide-callout
----------------------

The #pragma provide-callout statement is used in the callout module to inform mailfromd that the module has been loaded.

Do not use this pragma.

Data Types
==========

The mailfromd filter script language operates on entities of two types: numeric and string.

The numeric type is represented internally as a signed long integer.  Depending on the machine architecture, its size can vary. For example, on machines with Intel-based CPUs it is 32 bits long.

A string is a string of characters of arbitrary length. Strings can contain any characters except ASCII NUL.

There is also a generic pointer, which is designed to facilitate certain operations.  It appears only in body handler.  See body handler, for more information about it.

Numbers
=======

A decimal number is any sequence of decimal digits, not beginning with 0.

An octal number is 0 followed by any number of octal digits (0 through 7), for example: 0340.

A hex number is 0x or 0X followed by any number of hex digits (0 through 9 and a through f or A through F), for example: 0x3ef1.

Literals
========

A literal is any sequence of characters enclosed in single or double quotes.

After tempfail and reject actions two special kinds of literals are recognized: three-digit numeric values represent RFC 2821 reply codes, and literals consisting of tree digit groups separated by dots represent an extended reply code as per RFC 1893/2034.  For example:

     510   # A reply code
     5.7.1 # An extended reply code

Double-quoted strings
---------------------

String literals enclosed in double quotation marks (double-quoted strings) are subject to backslash interpretation, macro expansion, variable interpretation and back reference interpretation.

Backslash interpretation is performed at compilation time.  It consists in replacing the following escape sequences with the corresponding single characters:

Table: Backslash escapes

Sequence   Replaced with
\a   Audible bell character (ASCII 7)
\b   Backspace character (ASCII 8)
\f   Form-feed character (ASCII 12)
\n   Newline character (ASCII 10)
\r   Carriage return character (ASCII 13)
\t   Horizontal tabulation character (ASCII 9)
\v   Vertical tabulation character (ASCII 11)

In addition, the sequence \NEWLINE has the same effect as \n, for example:

     "a string with\
      embedded newline"
     "a string with\n embedded newline"

Any escape sequence of the form \xHH, where H denotes any hex digit is replaced with the character whose ASCII value is HH.  For example:

     "\x61nother" => "another"

Similarly, an escape sequence of the form \0OOO, where O is an octal digit, is replaced with the character whose ASCII value is OOO.

Macro expansion and variable interpretation occur at run-time.  During these phases all Sendmail macros (see Sendmail Macros), mailfromd variables (see Variables), and constants (see Constants) referenced in the string are replaced by their actual values.  For example, if the Sendmail macro f has the value postmaster@gnu.org.ua and the variable last_ip has the value 127.0.0.1, then the
string (Implementation note: actually, the references
are not interpreted within the string, instead, each such string is
split at compilation time into a series of concatenated atoms.  Thus,
our sample string will actually be compiled as:)

     $f . " last connected from " . last_ip . ";"

See Concatenation, for a description of this construct.  You can easily see how various strings are interpreted by using --dump-tree option (see --dump-tree).  In this case, it will produce:

       CONCAT:
         CONCAT:
           CONCAT:
             SYMBOL: f
             CONSTANT: " last connected from "
           VARIABLE last_ip (13)
         CONSTANT: ";"

     "$f last connected from %last_ip;"

will be expanded to

     "postmaster@gnu.org.ua last connected from 127.0.0.1;"

A back reference is a sequence \D, where D is a decimal number.  It refers to the Dth parenthesized subexpression in the last matches statement (The subexpressions are numbered by the positions of their opening parentheses, left to right.).  Any back reference occurring within a double-quoted string is replaced by the value of the corresponding subexpression.  See Special comparisons, for a detailed description of this process.  Back reference interpretation is performed at run time.

Single-quoted strings
---------------------

Any characters enclosed in single quotation marks are read unmodified.

The following examples contain pairs of equivalent strings:

     "a string"
     'a string'

     "\\(.*\\):"
     '\(.*\):'

Notice the last example.  Single quotes are particularly useful in writing regular expressions (see Special comparisons).

Here Documents
==============

Here-document is a special form of a string literal is, allowing to specify multiline strings without having to use backslash escapes.  The format of here-documents is:

     <<[FLAGS]WORD
     ...
     WORD

The <<WORD construct instructs the parser to read all the following lines up to the line containing only WORD, with possible trailing blanks.  The lines thus read are concatenated together into a single string.  For example:

     set str <<EOT
     A multiline
     string
     EOT

The body of a here-document is interpreted the same way as double-quoted strings (see Double-quoted strings).  For example, if Sendmail macro f has the value jsmith@some.com and the variable count is set to 10, then the following string:

     set s <<EOT
     <$f> has tried to send %count mails.
     Please see docs for more info.
     EOT

will be expanded to:

     <jsmith@some.com> has tried to send 10 mails.
     Please see docs for more info.

If the WORD is quoted, either by enclosing it in single quote characters or by prepending it with a backslash, all interpretations and expansions within the document body are suppressed.  For example:

     set s <<'EOT'
     The following line is read verbatim:
     <$f> has tried to send %count mails.
     Please see docs for more info.
     EOT

Optional FLAGS in the here-document construct control the way leading white space is handled.  If FLAGS is - (a dash), then all leading tab characters are stripped from input lines and the line containing WORD.  Furthermore, if - is followed by a single space, all leading whitespace is stripped from them.  This allows here-documents within configuration scripts to be indented in a natural fashion.  Examples:

     <<- TEXT
         <$f> has tried to send %count mails.
         Please see docs for more info.
     TEXT

Here-documents are particularly useful with reject actions (see reject.

Sendmail Macros
===============

Sendmail macros are referenced exactly the same way they are in sendmail.cf configuration file, i.e. $NAME, where NAME represents the macro name.  Notice, that the notation is the same for both single-character and multi-character macro names. For consistency with the Sendmail configuration the ${NAME} notation is also accepted.

Another way to reference Sendmail macros is by using function getmacro (see Macro access).

Sendmail macros evaluate to string values.

Notice, that to reference a macro, you must properly export it in your MTA configuration.  Attempt to reference a not exported macro will result in raising a e_macroundef exception at the run time (see uncaught exceptions).

Constants
=========

A constant is a symbolic name for an MFL value. Constants are defined using const statement:

     [QUALIFIER] const NAME EXPR

where NAME is an identifier, and EXPR is any valid MFL expression evaluating immediately to a constant literal or numeric value.  Optional QUALIFIER defines the scope of visibility for that constant (see scope of visibility): either public or static.

Once defined, any appearance of NAME in the program text is replaced by its value.  For example:

     const x 10/5
     const text "X is "

defines the numeric constant x with the value 5, and the literal constant text with the value X is .

A special construct is provided to define a series of numeric constants (an enumeration):

     [QUALIFIER] const
     do
       NAME0 [EXPR0]
       NAME1 [EXPR1]
       ...
       NAMEN [EXPRN]
     done

Each EXPRN, if present, must evaluate to a constant numeric expression.  The resulting value will be assigned to constant NAMEN.  If EXPRN is not supplied, the constant will be defined to the value of the previons constant plus one.  If EXPR0 is not supplied, 0 is assumed.

For example, consider the following statement

     const
     do
       A
       B
       C 10
       D
     done

This defines A to 0, B to 1, C to 10 and D to 11.

As a matter of fact, EXPRN may also evaluate to a constant string expression, provided that all expressions in the enumeration const statement are provided.  That is, the following is correct:

     const
     do
       A "one"
       B "two"
       C "three"
       D "four"
     done

whereas the following is not:

     const
     do
       A "one"
       B
       C "three"
       D "four"
     done

Trying to compile the latter example will produce:

     mailfromd: FILENAME:5.3: initializer element is not numeric

which means that mailfromd was trying to create constant B with the value of A incremented by one, but was unable to do so, because the value in question was not numeric.

Constants can be used in normal MFL expressions as well as in literals.  To expand a constant within a literal string, prepend a percent sign to its name, e.g.:

     echo "New %text %x" => "New X is 2"

This way of expanding constants creates an ambiguity if there happen to be a variable of the same name as the constant. See variable--constant clashes, for more information of this case and ways to handle it.

Built-in constants
------------------

Several constants are built into the MFL compiler.  To discern them from user-defined ones, their names start and end with two underscores (__).

The following constants are defined in mailfromd version VERSION:

 -- Built-in constant: string __file__
     Expands to the name of the current source file.

 -- Built-in constant: string __function__
     Expands to the name of the current lexical context, i.e. the function or handler name.

 -- Built-in constant: string __git__
     This built-in constant is defined for alpha versions only. Its value is the Git tag of the recent commit corresponding to that version of the package.  If the release contains some uncommitted changes, the value of the __git__ constant ends with the suffix -dirty.

 -- Built-in constant: number __line__
     Expands to the current line number in the input source file.

 -- Built-in constant: number __major__
     Expands to the major version number.

     The following example uses __major__ constant to determine if some version-dependent feature can be used:

          if __major__ > 2
            # Use some version-specific feature
          fi

 -- Built-in constant: number __minor__
     Expands to the minor version number.

 -- Built-in constant: string __module__
     Expands to the name of the current module (see Modules).

 -- Built-in constant: string __package__
     Expands to the package name (mailfromd)

 -- Built-in constant: number __patch__
     For alpha versions and maintenance releases expands to the version patch level.  For stable versions, expands to 0.

 -- Built-in constant: string __defpreproc__
     Expands to the default external preprocessor command line, if the preprocessor is used, or to an empty string if it is not, e.g.:

          __defpreproc__ => "/usr/bin/m4 -s"

     See Preprocessor, for information on preprocessor and its features.

 -- Built-in constant: string __preproc__
     Expands to the current external preprocessor command line, if the preprocessor is used, or to an empty string if it is not.  Notice, that it equals __defpreproc__, unless the preprocessor was redefined using --preprocessor command line option (see --preprocessor).

 -- Built-in constant: string __version__
     Expands to the textual representation of the program version (e.g. 3.0.90)

 -- Built-in constant: string __defstatedir__
     Expands to the default state directory (see statedir).

 -- Built-in constant: string __statedir__
     Expands to the current value of the program state directory (see statedir).  Notice, that it is the same as __defstatedir__ unless the state directory was redefined at run time.

Built-in constants can be used as variables, this allows to expand them within strings or here-documents.  The following example illustrates the common practice used for debugging configuration scripts:

     func foo(number x)
     do
       echo "%__file__:%__line__: foo called with arg %x"
       ...
     done

If the function foo were called in line 28 of the script file /etc/mailfromd.mf, like this: foo(10), you will see the following string in your logs:

     /etc/mailfromd.mf:28: foo called with arg 10

Variables
=========

Variables represent regions of memory used to hold variable data. These memory regions are identified by variable names.  A variable name must begin with a letter or underscore and must consist of letters, digits and underscores.

Each variable is associated with its scope of visibility, which defines the part of source code where it can be used (see scope of visibility).  Depending on the scope, we discern three main classes of variables: public, static and automatic (or local).

Public variables have indefinite lexical scope, so they may be referred to anywhere in the program.  Static are variables visible only within their module (see Modules).  Automatic or local variables are visible only within the given function or handler.

Public and static variables are sometimes collectively called global.

These variable classes occupy separate namespaces, so that an automatic variable can have the same name as an existing public or static one.  In this case this variable is said to shadow its global counterpart.  All references to such a name will refer to the automatic variable until the end of its scope is reached, where the global one becomes visible again.

Likewise, a static variable may have the same name as a static variable defined in another module.  However, it may not have the same name as a public variable.

A variable is declared using the following syntax:

     [QUALIFIERS] TYPE NAME

where NAME is the variable name, TYPE is the type of the data it is supposed to hold.  It is string for string variables and number for numeric ones.

For example, this is a declaration of a string variable var:

     string var

If a variable declaration occurs within a function (see User-defined) or handler (see Handlers), it declares an automatic variable, local to this function or handler. Otherwise, it declares a global variable.

Optional QUALIFIERS are allowed only in global declarations, i.e. in the variable declarations that appear outside of functions.  They specify the scope of the variable.  The public qualifier declares the variable as public and the static qualifier declares it as static.  The default scope is public, unless specified otherwise in the module declaration (see module structure).

Additionally, QUALIFIERS may contain the word precious, which instructs the compiler to mark this variable as precious. (see precious variables).  The value of the precious variable is not affected by the SMTP RSET command.  If both scope qualifier and precious are used, they may appear in any order, e.g.:

     static precious string rcpt_list

or

     precious static string rcpt_list

Declaration can be followed by any valid MFL expression, which supplies the initial value or initializer for the variable, for example:

     string var "test"

A global variable declared without initializer is implicitly initialized to a null value: numeric variables assume initial value 0, string variable are initialized to empty string.

The value of an automatic variable declared without initializer is unspecified.  It is an error to use such variable prior to assigning it a value.

A variable is assigned a value using the set statement:

     set NAME EXPR

where NAME is the variable name and EXPR is a mailfromd expression (see Expressions).  The effect of this statement is that the EXPR is evaluated and the value it yields is assigned to the variable NAME.

If the set statement is located outside a function or handler definition, the EXPR must be a constant expression, i.e. the compiler should be able to evaluate it immediately. -xrefoptimizer.

It is not an error to assign a value to a variable that is not declared.  In this case the assignment first declares a global or automatic variable having the type of EXPR and then assigns a value to it. Automatic variable is created if the assignment occurs within a function or handler, global variable is declared if it occurs at topmost lexical level.  This is called implicit variable declaration.

In the MFL program, variables are referenced by their name.  When appearing inside a double-quoted string, variables are referenced using the notation %NAME.  Any variable being referenced must have been declared earlier (either explicitly or implicitly).

Predefined Variables
--------------------

Several variables are predefined.  In mailfromd version VERSION these are:

 -- Variable: Predefined Variable number cache_used
     This variable is set by stdpoll and strictpoll built-ins (and, consequently, by the on poll statement).  Its value is 1 if the function used the cached data instead of directly polling the host, and 0 if the polling took place. See SMTP Callout functions.

     You can use this variable to make your reject message more informative for the remote party.  The common paradigm is to define a function, returning empty string if the result was obtained from polling, or some notice if cached data were used, and to use the function in the reject text, for example:

          func cachestr() returns string
          do
            if cache_used
              return "[CACHED] "
            else
              return ""
            fi
          done

     Then, in prog envfrom one can use:

          on poll $f
          do
          when not_found or failure:
            reject 550 5.1.0 cachestr() . "Sender validity not confirmed"
          done

 -- Predefined Variable: string clamav_virus_name
     Name of virus identified by ClamAV.  Set by clamav function (see ClamAV).

 -- Predefined Variable: number greylist_seconds_left
     Number of seconds left to the end of greylisting period.  Set by greylist and is_greylisted functions (see Special test functions).

 -- Predefined Variable: string ehlo_domain
     Name of the domain used by polling functions in SMTP EHLO or HELO command.  Default value is the fully qualified domain name of the host where mailfromd is run. See Polling.

 -- Variable: Predefined Variable string last_poll_greeting
     Callout functions (see SMTP Callout functions) set this variable before returning.  It contains the initial SMTP reply from the last polled host.

 -- Variable: Predefined Variable string last_poll_helo
     Callout functions (see SMTP Callout functions) set this variable before returning.  It contains the reply to the HELO (EHLO) command, received from the last polled host.

 -- Variable: Predefined Variable string last_poll_host
     Callout functions (see SMTP Callout functions) set this variable before returning.  It contains the host name or IP address of the last polled host.

 -- Variable: Predefined Variable string last_poll_recv
     Callout functions (see SMTP Callout functions) set this variable before returning.  It contains the last SMTP reply received from the remote host.  In case of multi-line replies, only the first line is stored.  If nothing was received the variable contains the string nothing.

 -- Variable: Predefined Variable string last_poll_sent
     Callout functions (see SMTP Callout functions) set this variable before returning.  It contains the last SMTP command sent to the polled host.  If nothing was sent, last_poll_sent contains the string nothing.

 -- Predefined Variable: string mailfrom_address
     Email address used by polling functions in SMTP MAIL FROM command (see Polling.).  Default is <>.  Here is an example of how to change it:

          set mailfrom_address "postmaster@my.domain.com"

     You can set this value to a comma-separated list of email addresses, in which case the probing will try each address until either the remote party accepts it or the list of addresses is exhausted, whichever happens first.

     It is not necessary to enclose emails in angle brackets, as they will be added automatically where appropriate.  The only exception is null return address, when used in a list of addresses.  In this case, it should always be written as <>.  For example:

          set mailfrom_address "postmaster@my.domain.com, <>"

 -- Predefined Variable: number sa_code
     Spam score for the message, set by sa function (see sa).

 -- Predefined Variable: number rcpt_count
     The variable rcpt_count keeps the number of recipients given so far by RCPT TO commands.  It is defined only in envrcpt handlers.

 -- Predefined Variable: number sa_threshold
     Spam threshold, set by sa function (see sa).

 -- Predefined Variable: string sa_keywords
     Spam keywords for the message, set by sa function (see sa).

 -- Predefined Variable: number safedb_verbose
     This variable controls the verbosity of the exception-safe database functions.  See safedb_verbose.

Back references
===============

A back reference is a sequence \D, where D is a decimal number.  It refers to the Dth parenthesized subexpression in the last matches statement (The subexpressions are numbered by the positions of their opening parentheses, left to right.).  Any back reference occurring within a double-quoted string is replaced with the value of the corresponding subexpression.  For example:

     if $f matches '.*@\(.*\)\.gnu\.org\.ua'
       set host \1
     fi

If the value of f macro is smith@unza.gnu.org.ua, the above code will assign the string unza to the variable host.

Notice, that each occurrence of matches will reset the table of back references, so try to use them as early as possible.  The following example illustrates a common error, when the back reference is used after the reference table has been reused by another matching:

     # Wrong!
     if $f matches '.*@\(.*\)\.gnu\.org\.ua'
       if $f matches 'some.*'
         set host \1
       fi
     fi

This will produce the following run time error:

     mailfromd: RUNTIME ERROR near file.mf:3: Invalid back-reference number

because the inner match (some.*) does not have any parenthesized subexpressions.

See Special comparisons, for more information about matches operator.

Handlers
========

Milter stage handler (or handler, for short) is a subroutine responsible for processing a particular milter state. There are eight handlers available.  Their order of invocation and arguments are described in milter-control-flow.

A handler is defined using the following construct:

     prog HANDLER-NAME
     do
       HANDLER-BODY
     done

where HANDLER-NAME is the name of the handler (see handler names), HANDLER-BODY is the list of filter statements composing the handler body.  Some handlers take arguments, which can be accessed within the HANDLER-BODY using the notation $N, where N is the ordinal number of the argument.  Here we describe the available handlers and their arguments:

 -- Handler: connect (string $1, number $2, number $3, string $4)

     Invocation:
          This handler is called once at the beginning of each SMTP connection.

     Arguments:

           1. string; The host name of the message sender, as reported by MTA.  Usually it is determined by a reverse lookup on the host address.  If the reverse lookup fails, $1 will contain the message sender's IP address enclosed in square brackets (e.g. [127.0.0.1]).

           2. number; Socket address family.  You need to require the status module to get symbolic definitions for the address families.  Supported families are:

               Table: Supported socket families

               Constant   Value   Meaning
               FAMILY_STDIO    0      Standard input/output (the MTA is
               run with -bs option)
               FAMILY_UNIX     1      UNIX socket
               FAMILY_INET     2      IPv4 protocol
               FAMILY_INET6    3      IPv6 protocol

           3. number; Port number if $2 is FAMILY_INET.

           4. string; Remote IP address if $2 is FAMILY_INET or full file name of the socket if $2 is FAMILY_UNIX.  If $2 is FAMILY_STDIO, $4 is an empty string.

     The actions (see Actions) appearing in this handler are handled by Sendmail in a special way.  First of all, any textual message is ignored.  Secondly, the only action that immediately closes the connection is tempfail 421.  Any other reply codes result in Sendmail switching to nullserver mode, where it accepts any commands, but answers with a failure to any of them, except for the following: QUIT, HELO, NOOP, which are processed as usual.

     The following table summarizes the Sendmail behavior depending on the action used:

     tempfail 421 EXCODE MESSAGE
          The caller is returned the following error message:

               421 4.7.0 HOSTNAME closing connection

          Both EXCODE and MESSAGE are ignored.

     tempfail 4XX EXCODE MESSAGE
          (where XX represents any digits, except 21) Both EXCODE and MESSAGE are ignored.  Sendmail switches to nullserver mode.  Any subsequent command, excepting the ones listed above, is answered with

               454 4.3.0 Please try again later

     reject 5XX EXCODE MESSAGE
          (where XX represents any digits).  All arguments are ignored.  Sendmail switches to nullserver mode.  Any subsequent command, excepting ones listed above, is answered with

               550 5.0.0 Command rejected

     Regarding reply codes, this behavior complies with RFC 2821 (section 3.9), which states:

          An SMTP server must not intentionally close the connection except:

          [...]

          -  After detecting the need to shut down the SMTP service and returning a 421 response code.  This response code can be issued after the server receives any command or, if necessary, asynchronously from command receipt (on the assumption that the client will receive it after the next command is issued).

     However, the RFC says nothing about textual messages and extended error codes, therefore Sendmail's ignoring of these is, in my opinion, absurd.  My practice shows that it is often reasonable, and even necessary, to return a meaningful textual message if the initial connection is declined.  The opinion of mailfromd users seems to support this view.  Bearing this in mind, mailfromd is shipped with a patch for Sendmail, which makes it honor both extended return code and textual message given with the action.  Two versions are provided: etc/sendmail-8.13.7.connect.diff, for Sendmail versions 8.13.x, and etc/sendmail-8.14.3.connect.diff, for Sendmail versions 8.14.3.

 -- Handler: helo (string $1)

     Invocation:
          This handler is called whenever the SMTP client sends HELO or EHLO command.  Depending on the actual MTA configuration, it can be called several times or even not at all.

     Arguments:

           1. string; Argument to HELO (EHLO) commands.

     Notes:
          According to RFC 28221, $1 must be domain name of the sending host, or, in case this is not available, its IP address enclosed in square brackets.  Be careful when taking decisions based on this value, because in practice many hosts send arbitrary strings. We recommend to use heloarg_test function (see heloarg_test) if you wish to analyze this value.

 -- Handler: envfrom (string $1, string $2)

     Invocation:
          Called when the SMTP client sends MAIL FROM command, i.e. once at the beginning of each message.

     Arguments:

           1. string; First argument to the MAIL FROM command, i.e. the email address of the sender.

           2. string; Rest of arguments to MAIL FROM separated by space character.  This argument can be "".

     Notes

           1. $1 is not the same as $f Sendmail variable, because the latter contains the sender email after address rewriting and normalization, while $1 contains exactly the value given by sending party.

           2. When the array type is implemented, $2 will contain an array of arguments.

 -- Handler: envrcpt (string $1, string $2)

     Invocation:
          Called once for each RCPT TO command, i.e. once for each recipient, immediately after envfrom.

     Arguments:

           1. string; First argument to the RCPT TO command, i.e. the email address of the recipient.

           2. string; Rest of arguments to RCPT TO separated by space character.  This argument can be "".

     Notes:
          When the array type is implemented, $2 will contain an array of arguments.

 -- Handler: data ()

     Invocation:
          Called after the MTA receives SMTP DATA command.  Notice that this handler is not supported by Sendmail versions prior to 8.14.0 and Postfix versions prior to 2.5.

     Arguments:
          None

 -- Handler: header (string $1, string $2)

     Invocation:
          Called once for each header line received after SMTP DATA command.

     Arguments:

           1. string; Header field name.

           2. string; Header field value.  The content of the header may include folded white space, i.e., multiple lines with following white space where lines are separated by LF (ASCII 10).  The trailing line terminator (CR/LF) is removed.

 -- Handler: eoh

     Invocation:
          This handler is called once per message, after all headers have been sent and processed.

     Arguments:
          None.

 -- Handler: body (pointer $1, number $2)

     Invocation:
          This header is called zero or more times, for each piece of the message body obtained from the remote host.

     Arguments:

           1. pointer; Piece of body text.  See Notes below.

           2. number; Length of data pointed to by $1, in bytes.

     Notes:
          The first argument points to the body chunk.  Its size may be quite considerable and passing it as a string may be costly both in terms of memory and execution time.  For this reason it is not passed as a string, but rather as a generic pointer, i.e. an object having the same size as number, which can be used to retrieve the actual contents of the body chunk if the need arises.

          A special function body_string is provided to convert this object to a regular MFL string (see Mail body functions).  Using it you can collect the entire body text into a single global variable, as illustrated by the following example:

               string text

               prog body
               do
                 set text text . body_string($1,$2)
               done

The text collected this way can then be used in the eom handler (see below) to parse and analyze it.

If you wish to analyze both the headers and mail body, the following code fragment will do that for you:

     string text

     # Collect all headers.
     prog header
     do
       set text text . $1 . ": " . $2 . "\n"
     done

     # Append terminating newline to the headers.
     prog eoh
     do
       set text "%text\n"
     done

     # Collect message body.
     prog body
     do
       set text text . body_string($1, $2)
     done

 -- Handler: eom

     Invocation:
          This handler is called once per message, when the terminating dot after DATA command has been received.

     Arguments:
          None

     Notes:
          This handler is useful for calling message capturing functions, such as sa or clamav.  For more information about these, refer to Interfaces to Third-Party Programs.

For your reference, the following table shows each handler with its arguments:

Table: State Handler Arguments

Handler   $1   $2   $3   $4
connect   Hostname   Socket Family   Port   Remote address
helo   HELO domain   N/A   N/A   N/A
envfrom   Sender email address   Rest of arguments   N/A   N/A
envrcpt   Recipient email address   Rest of arguments   N/A   N/A
header   Header name   Header value   N/A   N/A
eoh   N/A   N/A   N/A   N/A
body   Body segment (pointer)   Length of the segment
(numeric)   N/A   N/A
eom   N/A   N/A   N/A   N/A

The begin and end special handlers
==================================

Apart from the milter handlers described in the previous section, MFL defines two special handlers, called begin and end, which supply startup and cleanup instructions for the filter program.

The begin special handler is executed once for each SMTP session, after the connection has been established but before the first milter handler has been called.  Similarly, the end handler is executed exactly once, after the connection has been closed.  Neither of them takes any arguments.

The two handlers are defined using the following syntax:

     # Begin handler
     begin
     do
       ...
     done

     # End handler
     end
     do
       ...
     done

where ... represent any MFL statements.

An MFL program may have multiple begin and end definitions.  They can be intermixed with other definitions.  The compiler combines all begin statements into a single one, in the order they appear in the sources.  Similarly, all end blocks are concatenated together. The resulting begin is called once, at the beginning of each SMTP session, and end is called once at its termination.

Multiple begin and end handlers are a useful feature for writing modules (see Modules), because each module can thus have its own initialization and cleanup blocks.  Notice, however, that in this case the order in which subsequent begin and end blocks are executed is not defined.  It is only warranted that all begin blocks are executed at startup and all end blocks are executed at shutdown.  It is also warranted that all begin and end blocks defined within a compilation unit (i.e. a single abstract source file, with all #include and #include_once statements expanded in place) are executed in order of their appearance in the unit.

Due to their special nature, the startup and cleanup blocks impose certain restrictions on the statements that can be used within them:

 1. return cannot be used in begin and end handlers.

 2. The following Sendmail actions cannot be used in them: accept, continue, discard, reject, tempfail.  They can, however, be used in catch statements, declared in begin blocks (see example below).

 3. Header manipulation actions (see header manipulation) cannot be used in end handler.

The begin handlers are the usual place to put global initialization code to.  For example, if you do not want to use DNS caching, you can do it this way:

     begin
     do
       db_set_active("dns", 0)
     done

Additionally, you can set up global exception handling routines there.  For example, the following begin statement installs a handler for all exceptions not handled otherwise that logs the exception along with the stack trace and continues processing the message:

     begin
     do
       catch *
       do
         echo "Caught exception $1: $2"
         stack_trace()
         continue
       done
     done

Functions
=========

A function is a named mailfromd subroutine, which takes zero or more parameters and optionally returns a certain value.  Depending on the return value, functions can be subdivided into string functions and number functions. A function may have mandatory and optional parameters. When invoked, the function must be supplied exactly as many actual arguments as the number of its mandatory parameters.

Functions are invoked using the following syntax:

       NAME (ARGS)

where NAME is the function name and ARGS is a comma-separated list of expressions.  For example, the following are valid function calls:

       foo(10)
       interval("1 hour")
       greylist("/var/my.db", 180)

The number of parameters a function takes and their data types compose the function signature.  When actual arguments are passed to the function, they are converted to types of the corresponding formal parameters.

There are two major groups of functions: built-in functions, that are implemented in the mailfromd binary, and user-defined functions, that are written in MFL.  The invocation syntax is the same for both groups.

Mailfromd is shipped with a rich set of library functions.  These are described in Library.  In addition to these you can define your own functions.

Function definitions can appear anywhere between the handler declarations in a filter program, the only requirement being that the function definition occur before the place where the function is invoked.

The syntax of a function definition is:

     [QUALIFIER] func NAME (PARAM-DECL) returns DATA-TYPE
     do
       FUNCTION-BODY
     done

where NAME is the name of the function to define, PARAM-DECL is a comma-separated list of parameter declarations.  The syntax of the latter is the same as that of variable declarations (see Variable declarations), i.e.:

     TYPE NAME

declares the parameter NAME having the type TYPE.  The TYPE is string or number.

Optional QUALIFIER declares the scope of visibility for that function (see scope of visibility).  It is similar to that of variables, except that functions cannot be local (i.e. you cannot declare function within another function).

The public qualifier declares a function that may be referred to from any module, whereas the static qualifier declares a function that may be called only from the current module (see Modules).  The default scope is public, unless specified otherwise in the module declaration (see module structure).

For example, the following declares a function sum, that takes two numeric arguments and returns a numeric value:

     func sum(number x, number y) returns number

Similarly, the following is a declaration of a static function:

     static func sum(number x, number y) returns number

Parameters are referenced in the FUNCTION-BODY by their name, the same way as other variables.  Similarly, the value of a parameter can be altered using set statement.

A function can be declared to take a certain number of optional arguments.  In a function declaration, optional abstract arguments must be placed after the mandatory ones, and must be separated from them with a semicolon.  The following example is a definition of function foo, which takes two mandatory and two optional arguments:

     func foo(string msg, string email; number x, string pfx)

Mandatory parameters are: msg and email.  Optional parameters are: x and pfx.  The actual number of arguments supplied to the function is returned by a special construct $#.  In addition, the special construct @ARG evaluates to the ordinal number of variable ARG in the list of formal parameters (the first argument has number 0).  These two constructs can be used to verify whether an argument is supplied to the function.

When an actual argument for parameter n is supplied, the number of actual arguments ($#) is greater than the ordinal number of that parameter in the declaration list (@N).  Thus, the following construct can be used to check if an optional argument ARG is actually supplied:

     func foo(string msg, string email; number x, string arg)
     do
       if $# > @arg
         ...
       fi

The default mailfromd installation provides a special macro for this purpose: see defined.  Using it, the example above could be rewritten as:

     func foo(string msg, string email; number x, string arg)
     do
       if defined(arg)
         ...
       fi

Within a function body, optional arguments are referenced exactly the same way as the mandatory ones.  Attempt to dereference an optional argument for which no actual parameter was supplied, results in an undefined value, so be sure to check whether a parameter is passed before dereferencing it.

A function can also take variable number of arguments (such functions are called variadic).  This is indicated by the use of ellipsis as the last abstract parameter.  The statement below defines a function foo taking one mandatory, one optional and any number of additional arguments:

     func foo (string a ; string b, ...)

All actual arguments passed in a list of variable arguments are coerced to string data type.  To refer to these arguments in the function body, the following construct is used:

     $(EXPR)

where EXPR is any valid MFL expression, evaluating to a number N.  This construct refers to the value of Nth actual parameter from the variable argument list.  Parameters are numbered from 1, so the first variable parameter is $(1), and the last one is $($# - NM - NO), where NM and NO are numbers of mandatory and optional parameters to the function.

For example, the function below prints all its arguments:

     func pargs (string text, ...)
     do
       echo "text=%text"
       loop for number i 1,
            while i <= $# - 1,
            set i i + 1
       do
         echo "arg %i=" . $(i)
       done
     done

Note the loop limits.  The last variable argument has number $# - 1, because the function takes one mandatory argument.

The FUNCTION-BODY is any list of valid mailfromd statements.  In addition to the statements discussed below (see Statements) it can also contain the return statement, which is used to return a value from the function.  The syntax of the return statement is

       return VALUE

As an example of this, consider the following code snippet that defines the function sum to return a sum of its two arguments:

     func sum(number x, number y) returns number
     do
             return x + y
     done

The returns part in the function declaration is optional.  A declaration lacking it defines a procedure, or void function, i.e. a function that is not supposed to return any value. Such functions cannot be used in expressions, instead they are used as statements (see Statements).  The following example shows a function that emits a customized temporary failure notice:

     func stdtf()
     do
       tempfail 451 4.3.5 "Try again later"
     done

A function may have several names.  An alternative name (or alias) can be assigned to a function by using alias keyword, placed after PARAM-DECL part, for example:

     func foo()
     alias bar
     returns string
     do
       ...
     done

After this declaration, both foo() and bar() will refer to the same function.

The number of function aliases is unlimited.  The following fragment declares a function having three names:

     func foo()
     alias bar
     alias baz
     returns string
     do
       ...
     done

Although this feature is rarely needed, there are sometimes cases when it may be necessary.

A variable declared within a function becomes a local variable to this function.  Its lexical scope ends with the terminating done statement.

Parameters, local variables and global variables are using separate namespaces, so a parameter name can coincide with the name of a global, in which case a parameter is said to shadow the global.  All references to its name will refer to the parameter, until the end of its scope is reached, where the global one becomes visible again.  Consider the following example:

     number x

     func foo(string x)
     do
       echo "foo: %x"
     done

     prog envfrom
     do
       set x "Global"
       foo("Local")
       echo x
     done

Running mailfromd --test with this configuration will display:

     foo: Local
     Global

Some Useful Functions
---------------------

To illustrate the concept of user-defined functions, this subsection shows the definitions of some of the library functions shipped with mailfromd (Notice that these are intended for
educational purposes and do not necessarily coincide with the actual
definitions of these functions in Mailfromd version VERSION.). These functions are contained in modules installed along with the mailfromd binary.  To use any of them in your code, require the appropriate module as described in import, e.g. to use the revip function, do require 'revip'.

Functions and their definitions:

 1. revip

     The function revip (see revip) is implemented as follows:

          func revip(string ip) returns string
          do
            return inet_ntoa(ntohl(inet_aton(ip)))
          done

     Previously it was implemented using regular expressions.  Below we include this variant as well, as an illustration for the use of regular expressions:

          #pragma regex push +extended
          func revip(string ip) returns string
          do
            if ip matches '([0-9]+)\.([0-9]+)\.([0-9]+)\.([0-9]+)'
              return "\4.\3.\2.\1"
            fi
            return ip
          done
          #pragma regex pop

 2. strip_domain_part

     This function returns at most N last components of the domain name DOMAIN (see strip_domain_part).

          #pragma regex push +extended

          func strip_domain_part(string domain, number n) returns string
          do
            if n > 0 and
              domain matches '.*((\.[^.]+){' . $2 . '})'
              return substring(\1, 1, -1)
            else
              return domain
            fi
          done
          #pragma regex pop

 3. valid_domain

     See valid_domain, for a description of this function.  Its definition follows:

          require dns

          func valid_domain(string domain) returns number
          do
            return not (resolve(domain) = "0" and not hasmx(domain))
          done

 4. match_dnsbl

     The function match_dnsbl (see match_dnsbl) is defined as follows:

          require dns
          require match_cidr
          #pragma regex push +extended

          func match_dnsbl(string address, string zone, string range)
              returns number
          do
            string rbl_ip
            if range = 'ANY'
              set rbl_ip '127.0.0.0/8'
            else
              set rbl_ip range
              if not range matches '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
                return 0
              fi
            fi

            if not (address matches '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
                    and address != range)
              return 0
            fi

            if address matches
                  '^([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})$'
              if match_cidr (resolve ("\4.\3.\2.\1", zone), rbl_ip)
                return 1
              else
                return 0
              fi
            fi
            # never reached
          done

Expressions
===========

Expressions are language constructs, that evaluate to a value, that can subsequently be echoed, tested in a conditional statement, assigned to a variable or passed to a function.

Constant Expressions
--------------------

Literals and numbers are constant expressions.  They evaluate to string and numeric types.

Function Calls
--------------

A function call is an expression.  Its type is the return type of the function.

Concatenation
-------------

Concatenation operator is . (a dot).  For example, if $f is smith, and $client_addr is 10.10.1.1, then:

     $f . "-" . $client_addr => "smith-10.10.1.1"

Any two adjacent literal strings are concatenated, producing a new string, e.g.

     "GNU's" " not " "UNIX" => "GNU's not UNIX"

Arithmetic Operations
---------------------

The filter script language offers the common arithmetic operators: +, -, * and /.  In addition, the % is a modulo operator, i.e. it computes the remainder of division of its operands.

All of them follow usual precedence rules and work as you would expect them to.

Bitwise shifts
--------------

The << represents a bitwise shift left operation, which shifts the binary representation of the operand on its left by the number of bits given by the operand on its right.

Similarly, the >> represents a bitwise shift right.

Relational Expressions
----------------------

Relational expressions are:

Table: Relational Expressions

Expression   Result
X < Y   True if X is less than Y.
X <= Y   True if X is less than or equal to Y.
X > Y   True if X is greater than Y.
X >= Y   True if X is greater than or equal to Y.
X = Y   True if X is equal to Y.
X != Y   True if X is not equal to Y.

The relational expressions apply to string as well as to numbers. When a relational operation applies to strings, case-sensitive comparison is used, e.g.:

     "String" = "string" => False
     "String" < "string" => True

Special Comparisons
-------------------

In addition to the traditional relational operators, described above, mailfromd provides two operators for regular expression matching:

Table: Regular Expression Matching

Expression   Result
X matches Y   True if the string X matches the
regexp denoted by Y.
X fnmatches Y   True if the string X matches the
globbing pattern denoted by Y.

The type of the regular expression used by matches operator is controlled by #pragma regex (see pragma regex).  For example:

     $f => "gray@gnu.org.ua"
     $f matches '.*@gnu\.org\.ua' => true
     $f matches '.*@GNU\.ORG\.UA' => false
     #pragma regex +icase
     $f matches '.*@GNU\.ORG\.UA' => true

The fnmatches operator compares its left-hand operand with a globbing pattern (see glob(7)) given as its right-hand side operand.  For example:

     $f => "gray@gnu.org.ua"
     $f fnmatches "*ua" => true
     $f fnmatches "*org" => false
     $f fnmatches "*org*" => true

Both operators have a special form, for MX pattern matching. The expression:

       X mx matches Y

is evaluated as follows: first, the expression X is analyzed and, if it is an email address, its domain part is selected.  If it is not, its value is used verbatim.  Then the list of MXs for this domain is looked up.  Each of MX names is then compared with the regular expression Y.  If any of the names matches, the expression returns true.  Otherwise, its result is false.

Similarly, the expression:

       X mx fnmatches Y

returns true only if any of the MXs for (domain or email) X match the globbing pattern Y.

Both mx matches and mx fnmatches can signal the following exceptions: e_temp_failure, e_failure.

The value of any parenthesized subexpression occurring within the right-hand side argument to matches or mx matches can be referenced using the notation \D, where D is the ordinal number of the subexpression (subexpressions are numbered from left to right, starting at 1).  This notation is allowed in the program text as well as within double-quoted strings and here-documents, for example:

     if $f matches '.*@\(.*\)\.gnu\.org\.ua'
       set message "Your host name is \1;"
     fi

Remember that the grouping symbols are \( and \) for basic regular expressions, and ( and ) for extended regular expressions.  Also make sure you properly escape all special characters (backslashes in particular) in double-quoted strings, or use single-quoted strings to avoid having to do so (see singe-vs-double, for a comparison of the two forms).

Boolean Expressions
-------------------

A boolean expression is a combination of relational or matching expressions using the boolean operators and, or and not, and, eventually, parentheses to control nesting:

table: Boolean Operators

Expression   Result
X and Y   True only if both X and
Y are true.
X or Y   True if any of X or Y
is true.
not X   True if X is false.

Binary boolean expressions are computed using shortcut evaluation:

X and Y
     If X => false, the result is false and Y is not evaluated.

X or Y
     If X => true, the result is true and Y is not evaluated.

Operator Precedence
-------------------

Operator precedence is an abstract value associated with each language operator, that determines the order in which operators are executed when they appear together within a single expression. Operators with higher precedence are executed first.  For example, * has a higher precedence than +, therefore the expression a + b * c is evaluated in the following order: first b is multiplied by c, then a is added to the product.

When operators of equal precedence are used together they are evaluated from left to right (i.e., they are left-associative), except for comparison operators, which are non-associative (these are explicitly marked as such in the table below).  This means that you cannot write:

     if 5 <= x <= 10

Instead, you should write:

     if 5 <= x and x <= 10

The precedences of the mailfromd operators where selected
so as to match that used in most programming languages. (The
only exception is not, whose precedence in MFL is
much lower than usual (in most programming languages it has the same
precedence as unary -).  This allows to write conditional
expressions in more understandable manner.  Consider the following
condition:)

     if not x < 2 and y = 3

It is understood as ``if x is not less than 2 and y equals 3'', whereas with the usual precedence for not it would have meant ``if negated x is less than 2 and y equals 3''.

The following table lists all operators in order of decreasing precedence:

(...)
     Grouping

$ %
     Sendmail macros and mailfromd variables

* /
     Multiplication, division

+ -
     Addition, subtraction

<< >>
     Bitwise shift left and right

< <= >= >
     Relational operators (non-associative)

= != matches fnmatches
     Equality and special comparison (non-associative)

&
     Logical (bitwise) AND

^
     Logical (bitwise) XOR

|
     Logical (bitwise) OR

not
     Boolean negation

and
     Logical and.

or
     Logical or

.
     String concatenation

Type Casting
------------

When two operands on each side of a binary expression have different type, mailfromd evaluator coerces them to a common type.  This is known as implicit type casting.  The rules for implicit type casting are:

 1. Both arguments to an arithmetical operation are cast to numeric type.

 2. Both arguments to the concatenation operation are cast to string.

 3. Both arguments to `match' or `fnmatch' function are cast to string.

 4. The argument of the unary negation (arithmetical or boolean) is cast to numeric.

 5. Otherwise the right-hand side argument is cast to the type of the left-hand side argument.

The construct for explicit type cast is:

     TYPE(EXPR)

where TYPE is the name of the type to coerce EXPR to.  For example:

     string(2 + 4*8) => "34"

Variable and Constant Shadowing
===============================

When any two named entities happen to have the same name we say that a name clash occurs.  The handling of name clashes depends on types of the entities involved in it.

function -- any
---------------

A name of a constant or variable can coincide with that of a function, it does not produce any warnings or errors because functions, variables and constants use different namespaces.  For example, the following code is correct:

     const a 4

     func a()
     do
       echo a
     done

When executed, it prints 4.

function -- function, handler -- function, and function -- handler
------------------------------------------------------------------

Redefinition of a function or using a predefined handler name (see Handlers) as a function name results in a fatal error.  For example, compiling this code:

     func a()
     do
       echo "1"
     done

     func a()
     do
       echo "2"
     done

causes the following error message:

     mailfromd: sample.mf:9: syntax error, unexpected
     FUNCTION_PROC, expecting IDENTIFIER

handler -- variable
-------------------

A variable name can coincide with a handler name.  For example, the following code is perfectly OK:

     string envfrom "M"
     prog envfrom
     do
             echo envfrom
     done

handler -- handler
------------------

If two handlers with the same name are defined, the definition that appears further in the source text replaces the previous one.  A warning message is issued, indicating locations of both definitions, e.g.:

     mailfromd: sample.mf:116: Warning: Redefinition of handler
     `envfrom'
     mailfromd: sample.mf:34: Warning: This is the location of the
     previous definition

variable -- variable
--------------------

Defining a variable having the same name as an already defined one results in a warning message being displayed.  The compilation succeeds.  The second variable shadows the first, that is any subsequent references to the variable name will refer to the second variable. For example:

     string x "Text"
     number x 1

     prog envfrom
     do
       echo x
     done

Compiling this code results in the following diagnostics:

     mailfromd: sample.mf:4: Redeclaring `x' as different data type
     mailfromd: sample.mf:2: This is the location of the previous
     definition

Executing it prints 1, i.e. the value of the last definition of x.

The scope of the shadowing depends on storage classes of the two variables.  If both of them have external storage class (i.e. are global ones), the shadowing remains in effect until the end of input. In other words, the previous definition of the variable is effectively forgotten.

If the previous definition is a global, and the shadowing definition is an automatic variable or a function parameter, the scope of this shadowing ends with the scope of the second variable, after which the previous definition (global) becomes visible again.  Consider the following code:

     set x "initial"

     func foo(string x) returns string
     do
       return x
     done

     prog envfrom
     do
       echo foo("param")
       echo x
     done

Its compilation produces the following warning:

     mailfromd: sample.mf:3: Warning: Parameter `x' is shadowing a global

When executed, it produces the following output:

     param
     initial
     State envfrom: continue

variable -- constant
--------------------

If a constant is defined which has the same name as a previously defined variable (the constant shadows the variable), the compiler prints the following diagnostic message:

     FILE:LINE: Warning: Constant name `NAME' clashes with a variable name
     FILE:LINE: Warning: This is the location of the previous definition

A similar diagnostics is issued if a variable is defined whose name coincides with a previously defined constant (the variable shadows the constant).

In any case, any subsequent notation %NAME refers to the last defined symbol, be it variable or constant.

Notice, that shadowing occurs only when using %NAME notation. Referring to the constant using its name without % allows to avoid shadowing effects.

If a variable shadows a constant, the scope of the shadowing depends on the storage class of the variable.  For automatic variables and function parameters, it ends with the final done closing the function.  For global variables, it lasts up to the end of input.

For example, consider the following code:

     const a 4

     func foo(string a)
     do
       echo a
     done

     prog envfrom
     do
       foo(10)
       echo a
     done

When run, it produces the following output:

     $ mailfromd --test sample.mf
     mailfromd: sample.mf:3: Warning: Variable name `a' clashes with a
     constant name
     mailfromd: sample.mf:1: Warning: This is the location of the previous
     definition
     10
     4
     State envfrom: continue

constant -- constant
--------------------

Redefining a constant produces a warning message.  The latter definition shadows the former.  Shadowing remains in effect until the end of input.

Statements
==========

Statements are language constructs, that, unlike expressions, do not return any value.  Statements execute some actions, such as assigning a value to a variable, or serve to control the execution flow in the program.

Action Statements
-----------------

An action statement instructs mailfromd to perform a certain action over the message being processed.  There are two kinds of actions: return actions and header manipulation actions.

Reply Actions
.............

Reply actions tell Sendmail to return given response code to the remote party.  There are five such actions:

accept
     Return an accept reply.  The remote party will continue transmitting its message.

reject CODE EXCODE MESSAGE-EXPR
reject (CODE-EXPR, EXCODE-EXPR, MESSAGE-EXPR)
     Return a reject reply.  The remote party will have to cancel transmitting its message.  The three arguments are optional, their usage is described below.

tempfail CODE EXCODE MESSAGE
tempfail (CODE-EXPR, EXCODE-EXPR, MESSAGE-EXPR)
     Return a temporary failure reply.  The remote party can retry to send its message later.  The three arguments are optional, their usage is described below.

discard
     Instructs Sendmail to accept the message and silently discard it without delivering it to any recipient.

continue
     Stops the current handler and instructs Sendmail to continue processing of the message.

Two actions, reject and tempfail can take up to three optional parameters.  There are two forms of supplying these parameters.

In the first form, called literal or traditional notation, the arguments are supplied as additional words after the action name, and are separated by whitespace.   The first argument is a three-digit RFC 2821 reply code.  It must begin with 5 for reject and with 4 for tempfail.  If two arguments are supplied, the second argument must be either an extended reply code (RFC 1893/2034) or a textual string to be returned along with the SMTP reply.  Finally, if all three arguments are supplied, then the second one must be an extended reply code and the third one must give the textual string.  The following examples illustrate the possible ways of using the reject statement:

     reject
     reject 503
     reject 503 5.0.0
     reject 503 "Need HELO command"
     reject 503 5.0.0 "Need HELO command"

The notion textual string, used above means either a literal string or an MFL expression that evaluates to string. However, both code and extended code must always be literal.

The second form of supplying arguments is called functional notation, because it resembles the function syntax.  When used in this form, the action word is followed by a parenthesized group of exactly three arguments, separated by commas.  Each argument is a MFL expression.  The meaning and ordering of the arguments is the same as in literal form.  Any or all of these three arguments may be absent, in which case it will be replaced by the default value.  To illustrate this, here are the statements from the previous example, written in functional notation:

     reject(,,)
     reject(503,,)
     reject(503, 5.0.0)
     reject(503, , "Need HELO command")
     reject(503, 5.0.0, "Need HELO command")

Notice that there is an important difference between the two notations.  The functional notation allows to compute both reply codes at run time, e.g.:

       reject(500 + dig2*10 + dig3, "5.%edig2.%edig2")

Header Actions
..............

Header manipulation actions provide basic means to add, delete or modify the message RFC 2822 headers.

add NAME STRING
     Add the header NAME with the value STRING.  E.g.:

          add "X-Seen-By" "Mailfromd VERSION"

     (notice argument quoting)

replace NAME STRING
     The same as add, but if the header NAME already exists, it will be removed first, for example:

          replace "X-Last-Processor" "Mailfromd VERSION"

delete NAME
     Delete the header named NAME:

          delete "X-Envelope-Date"

These actions impose some restrictions.  First of all, their first argument must be a literal string (not a variable or expression). Secondly, there is no way to select a particular header instance to delete or replace, which may be necessary to properly handle multiple headers (e.g. Received).  For more elaborate ways of header modifications, see Header modification functions.

Variable Assignments
--------------------

An assignment is a special statement that assigns a value to the variable.  It has the following syntax:

     set NAME VALUE

where NAME is the variable name and VALUE is the value to be assigned to it.

Assignment statements can appear in any part of a filter program. If an assignment occurs outside of function or handler definition, the VALUE must be a literal value (see Literals).  If it occurs within a function or handler definition, VALUE can be any valid mailfromd expression (see Expressions).  In this case, the expression will be evaluated and its value will be assigned to the variable.  For example:

     set delay 150

     prog envfrom
     do
       set delay delay * 2
       ...
     done

The pass statement
------------------

The pass statement has no effect.  It is used in places where no statement is needed, but the language syntax requires one:

     on poll $f do
     when success:
       pass
     when not_found or failure:
       reject 550
     done

The echo statement
------------------

The echo statement concatenates all its arguments into a single string and sends it to the syslog using the priority info.  It is useful for debugging your script, in conjunction with built-in constants (see Built-in constants), for example:

     func foo(number x)
     do
       echo "%__file__:%__line__: foo called with arg %x"
       ...
     done

Conditional Statements
======================

Conditional expressions, or conditionals for short, test some conditions and alter the control flow depending on the result.  There are two kinds of conditional statements: if-else branches and switch statements.

The syntax of an if-else branching construct is:

       if CONDITION THEN-BODY [else ELSE-BODY] fi

Here, CONDITION is an expression that governs control flow within the statement.  Both THEN-BODY and ELSE-BODY are lists of mailfromd statements.  If CONDITION is true, THEN-BODY is executed, if it is false, ELSE-BODY is executed.  The else part of the statement is optional.  The condition is considered false if it evaluates to zero, otherwise it is considered true.  For example:

     if $f = ""
       accept
     else
       reject
     fi

This will accept the message if the value of the Sendmail macro $f is an empty string, and reject it otherwise.  Both THEN-BODY and ELSE-BODY can be compound statements including other if statements.  Nesting level of conditional statements is not limited.

To facilitate writing complex conditional statements, the elif keyword can be used to introduce alternative conditions, for example:

     if $f = ""
       accept
     elif $f = "root"
       echo "Mail from root!"
     else
       reject
     fi

Another type of branching instruction is switch statement:

     switch CONDITION
     do
     case X1 [or X2 ...]:
       STMT1
     case Y1 [or Y2 ...]:
       STMT2
       .
       .
       .
     [default:
       STMT]
     done

Here, X1, X2, Y1, Y2 are literal expressions; STMT1, STMT2 and STMT are arbitrary mailfromd statements (possibly compound); CONDITION is the controlling expression.  The vertical dotted row represent another eventual case branches.

This statement is executed as follows: the CONDITION expression is evaluated and if its value equals X1 or X2 (or any other X from the first case), then STMT1 is executed.  Otherwise, if  CONDITION evaluates to Y1 or Y2 (or any other Y from the second case), then STMT2 is executed.  Other case branches are tried in turn.  If none of them matches, STMT (called the default branch) is executed.

There can be as many case branches as you wish.  The default branch is optional.  There can be at most one default branch.

An example of switch statement follows:

     switch x
     do
     case 1 or 3:
       add "X-Branch" "1"
       accept
     case 2 or 4 or 6:
       add "X-Branch" "2"
     default:
       reject
     done

If the value of mailfromd variable x is 2 or 3, it will accept the message immediately, and add a X-Branch: 1 header to it.  If x equals 2 or 4 or 6, this code will add X-Branch: 2 header to the message and will continue processing it.  Otherwise, it will reject the message.

The controlling condition of a switch statement may evaluate to numeric or string type.  The type of the condition governs the type of comparisons used in case branches: for numeric types, numeric equality will be used, whereas for string types, string equality is used.

Loop Statements
===============

The loop statement allows for repeated execution of a block of code, controlled by some conditional expression.  It has the following form:

     loop [LABEL]
          [for STMT1] [,while EXPR1] [,STMT2]
     do
       STMT3
     done [while EXPR2]

where STMT1, STMT2, and STMT3 are statement lists, EXPR1 and EXPR2 are expressions.

The control flow is as follows:

 1. If STMT1 is specified, execute it.

 2. Evaluate EXPR1.  If it is zero, go to 6.  Otherwise, continue.

 3. Execute STMT3.

 4. If STMT2 is supplied, execute it.

 5. If EXPR2 is given, evaluate it.  If it is zero, go to 6. Otherwise, go to 2.

 6. End.

Thus, STMT3 is executed until either EXPR1 or EXPR2 yield a zero value.

The loop body -- STMT3 -- can contain special statements:

break [LABEL]
     Terminates the loop immediately.  Control passes to 6 (End) in the formal definition above.  If LABEL is supplied, the statement terminates the loop statement marked with that label.  This allows to break from nested loops.

     It is similar to break statement in C or shell.

next [LABEL]
     Initiates next iteration of the loop.  Control passes to 4 in the formal definition above.  If LABEL is supplied, the statement starts next iteration of the loop statement marked with that label.  This allows to request next iteration of an upper-level loop from a nested loop statement.

The loop statement can be used to create iterative statements of arbitrary complexity.  Let's illustrate it in comparison with C.

The statement:

     loop
     do
       STMT-LIST
     done

creates an infinite loop.  The only way to exit from such a loop is to call break (or return, if used within a function), somewhere in STMT-LIST.

The following statement is equivalent to while (EXPR1) STMT-LIST in C:

     loop while EXPR
     do
       STMT-LIST
     done

The C construct for (EXPR1; EXPR2; EXPR3) is written in MFL as follows:

     loop for STMT1, while EXPR2, STMT2
     do
       STMT3
     done

For example, to repeat STMT3 10 times:

     loop for set i 0, while i < 10, set i i + 1
     do
       STMT3
     done

Finally, the C do loop is implemented as follows:

     loop
     do
       STMT-LIST
     done while EXPR

As a real-life example of a loop statement, let's consider the implementation of function ptr_validate, which takes a single argument IPSTR, and checks its validity using the following algorithm:

Perform a DNS reverse-mapping for IPSTR, looking up the corresponding PTR record in in-addr.arpa.  For each record returned, look up its IP addresses (A records).  If IPSTR is among the returned IP addresses, return 1 (true), otherwise return 0 (false).

The implementation of this function in MFL is:

     #pragma regex push +extended

     func ptr_validate(string ipstr) returns number
     do
       loop for string names dns_getname(ipstr) . " "
                number i index(names, " "),
            while i != -1,
            set names substr(names, i + 1)
            set i index(names, " ")
       do
         loop for string addrs dns_getaddr(substr(names, 0, i)) . " "
                  number j index(addrs, " "),
              while j != -1,
              set addrs substr(addrs, j + 1)
              set j index(addrs, " ")
         do
           if ipstr == substr(addrs, 0, j)
             return 1
           fi
         done
       done
       return 0
     done

Exceptional Conditions
======================

When the running program encounters a condition it is not able to handle, it signals an exception.  To illustrate the concept, let's consider the execution of the following code fragment:

       if primitive_hasmx(domainpart($f))
         accept
       fi

The function primitive_hasmx (see primitive_hasmx) tests whether the domain name given as its argument has any MX records.  It should return a boolean value.  However, when querying the Domain Name System, it may fail to get a definite result.  For example, the DNS server can be down or temporary unavailable.  In other words, primitive_hasmx can be in a situation when, instead of returning yes or no, it has to return don't know.  It has no way of doing so, therefore it signals an exception.

Each exception is identified by exception type, an integer number associated with it.

Built-in Exceptions
-------------------

The first MAX_E_EXCEPTIONS exception numbers are reserved for built-in exceptions.  These are declared in module status.mf. The following table summarizes all built-in exception types implemented by mailfromd version VERSION.  Exceptions are listed in lexicographic order.

e_badmmq
     The called function cannot finish its task because an uncompatible message modification function was called at some point before it. For details, MMQ and dkim_sign.

e_dbfailure
     General database failure.  For example, the database cannot be opened.  This exception can be signaled by any function that queries any DBM database.

e_divzero
     Division by zero.

e_exists
     This exception is emitted by dbinsert built-in if the requested key is already present in the database (see dbinsert).

e_eof
     Function reached end of file while reading.  See I/O functions, for a description of functions that can signal this exception.

e_failure
failure
e_failure
     A general failure has occurred.  In particular, this exception is signaled by DNS lookup functions when any permanent failure occurs. This exception can be signaled by any DNS-related function (hasmx, poll, etc.) or operation (mx matches).

e_format
     Invalid input format.  This exception is signaled if input data to a function are improperly formatted.  In version VERSION it is signaled by message_burst function if its input message is not formatted according to RFC 934.  See Message digest functions.

e_invcidr
     Invalid CIDR notation.  This is signaled by match_cidr function when its second argument is not a valid CIDR.

e_invip
     Invalid IP address.  This is signaled by match_cidr function when its first argument is not a valid IP address.

e_invtime
     Invalid time interval specification.  It is signaled by interval function if its argument is not a valid time interval (see time interval specification).

e_io
     An error occurred during the input-output operation.  See I/O functions, for a description of functions that can signal this exception.

e_macroundef
     A Sendmail macro is undefined.

e_noresolve
     The argument of a DNS-related function cannot be resolved to host name or IP address.  Currently only ismx (see ismx) raises this exception.

e_range
     The supplied argument is outside the allowed range.  This is signalled, for example, by substring function (see substring).

e_regcomp
     Regular expression cannot be compiled.  This can happen when a regular expression (a right-hand argument of a matches operator) is built at the runtime and the produced string is an invalid regex.

e_ston_conv
     String-to-number conversion failed.  This can be signaled when a string is used in numeric context which cannot be converted to the numeric data type.  For example:

           set x "10a"
           if x / 2
             ...

     The if condition will signal ston_conv, since 10a cannot be converted to a number.

e_temp_failure
temp_failure
e_temp_failure
     A temporary failure has occurred.  This can be signaled by DNS-related functions or operations.

e_url
     The supplied URL is invalid.  See Interfaces to Third-Party Programs.

In addition to these, two symbols are defined that are not exception types in the strict sense of the world, but are provided to make writing filter scripts more convenient.  These are success, meaning successful return from a function, and not_found, meaning that the required entity (e.g. domain name or email address) was not found.  See figure-poll-wrapper, for an illustration on how these can be used.  For consistency with other exception codes, these can be spelled as e_success and e_not_found.

User-defined Exceptions
-----------------------

You can define your own exception types using the dclex statement:

     dclex TYPE

In this statement, TYPE must be a valid MFL identifier, not used for another constant (see Constants). The dclex statement defines a new exception identified by the constant TYPE and allocates a new exception number for it.

The TYPE can subsequently be used in throw and catch statements, for example:

     dclex myrange

     number fact(number val)
       returns number
     do
       if val < 0
         throw myrange "fact argument is out of range"
       fi
       ...
     done

Exception Handling
------------------

Normally when an exception is signalled, the program execution is terminated and the MTA is returned a tempfail status.  Additional information regarding the exception is then output to the logging channel (see Logging and Debugging).  However, the user can intercept any exception by installing his own exception-handling routines.

An exception-handling routine is introduced by a try--catch statement, which has the following syntax:

     try
     do
       STMTLIST
     done
     catch EXCEPTION-LIST
     do
       HANDLER-BODY
     done

where STMTLIST and HANDLER-BODY are sequences of MFL statements and EXCEPTION-LIST is the list of exception types, separated by the word or.  A special EXCEPTION-LIST * is allowed and means all exceptions.

This construct works as follows.  First, the statements from STMTLIST are executed.  If the execution finishes successfully, control is passed to the first statement after the catch block.  Otherwise, if an exception is signalled and this exception is listed in EXCEPTION-LIST, the execution is passed to the HANDLER-BODY.  If the exception is not listed in EXCEPTION-LIST, it is handled as usual.

The following example shows a try--catch construct used for handling eventual exceptions, signalled by primitive_hasmx.

     try
     do
       if primitive_hasmx(domainpart($f))
         accept
       else
         reject
       fi
     done
     catch e_failure or e_temp_failure
     do
       echo "primitive_hasmx failed"
       continue
     done

The try--catch statement can appear anywhere inside a function or a handler, but it cannot appear outside of them.  It can also be nested within another try--catch, in either of its parts.  Upon exit from a function or milter handler, all exceptions are restored to the state they had when it has been entered.

A catch block can also be used alone, without preceding try part.  Such a construct is called a standalone catch.  It is mostly useful for setting global exception handlers in a begin statement (see begin/end).  When used within a usual function or handler, the exception handlers set by a standalone catch remain in force until either another standalone catch appears further in the same function or handler, or an end of the function is encountered, whichever occurs first.

A standalone catch defined within a function must return from it by executing return statement.  If it does not do that explicitly, the default value of 1 is returned.  A standalone catch defined within a milter handler must end execution with any of the following actions: accept, continue, discard, reject, tempfail.  By default, continue is used.

It is not recommended to mix try--catch constructs and standalone catches.  If a standalone catch appears within a try--catch statement, its scope of visibility is undefined.

Upon entry to a HANDLER-BODY, two implicit positional arguments are defined, which can be referenced in HANDLER-BODY as $1 and $2.  The first argument gives the numeric code of the exception that has occurred.  The second argument is a textual string containing a human-readable description of the exception.

The following is an improved version of the previous example, which uses these parameters to supply more information about the failure:

     try
     do
       if primitive_hasmx(domainpart($f))
         accept
       else
         reject
       fi
     done
     catch e_failure or e_temp_failure
     do
       echo "Caught exception $1: $2"
       continue
     done

The following example defines the function hasmx that returns true if the domain part of its argument has any MX records, and false if it does not or if an exception occurs  (This function is part of the mailfromd library, see hasmx.).

     func hasmx (string s)
       returns number
     do
       try
       do
         return primitive_hasmx(domainpart(s))
       done
       catch *
       do
         return 0
       done
     done

The same function can written using standalone catch:

     func hasmx (string s)
       returns number
     do
       catch *
       do
         return 0
       done
       return primitive_hasmx(domainpart(s))
     done

All variables remain visible within catch body, with the exception of positional arguments of the enclosing handler.  To access positional arguments of a handler from the catch body, assign them to local variables prior to the try--catch construct, e.g.:

     prog header
     do
       string hname $1
       string hvalue $2
       try
       do
         ...
       done
       catch *
       do
         echo "Exception $1 while processing header %hname: %hvalue"
         echo $2
         tempfail
       done

You can also generate (or raise) exceptions explicitly in the code, using throw statement:

     throw EXCODE DESCR

The arguments correspond exactly to the positional parameters of the catch statement: EXCODE gives the numeric code of the exception, DESCR gives its textual description.  This statement can be used in complex scripts to create non-local exits from deeply nested statements.  Elaborate on that.

Notice, that the the EXCODE argument must be an immediate value: an exception identifier (either a built-in one or one declared previously using a dclex statement).

Sender Verification Tests
=========================

The filter script language provides a wide variety of functions for sender address verification or polling, for short.  These functions, which were described in SMTP Callout functions, can be used to implement any sender verification method.  The additional data that can be needed is normally supplied by two global variables: ehlo_domain, keeping the default domain for the EHLO command, and mailfrom_address, which stores the sender address for probe messages (see Predefined variables).

For example, a simplest way to implement standard polling would be:

     prog envfrom
     do
       if stdpoll($1, ehlo_domain, mailfrom_address) == 0
         accept
       else
         reject 550 5.1.0 "Sender validity not confirmed"
       fi
     done

However, this does not take into account exceptions that stdpoll can signal.  To handle them, one will have to use catch, for example thus:

     require status

     prog envfrom
     do
       try
       do
         if stdpoll($1, ehlo_domain, mailfrom_address) == 0
           accept
         else
           reject 550 5.1.0 "Sender validity not confirmed"
         fi
       done
       catch e_failure or e_temp_failure
       do
         switch $1
         do
         case failure:
           reject 550 5.1.0 "Sender validity not confirmed"
         case temp_failure:
           tempfail 450 4.1.0 "Try again later"
         done
       done
     done

If polls are used often, one can define a wrapper function, and use it instead.  The following example illustrates this approach:

Figure: Building Poll Wrappers

     func poll_wrapper(string email) returns number
     do
       catch e_failure or e_temp_failure
       do
         return email
       done
       return stdpoll(email, ehlo_domain, mailfrom_address)
     done

     prog envfrom
     do
       switch poll_wrapper($f)
       do
       case success:
         accept
       case not_found or failure:
         reject 550 5.1.0 "Sender validity not confirmed"
       case temp_failure:
         tempfail 450 4.1.0 "Try again later"
       done
     done

Notice the way envfrom handles success and not_found, which are not exceptions in the strict sense of the word.

The above paradigm is so common that mailfromd provides a special language construct to simplify it: the on statement. Instead of manually writing the wrapper function and using it as a switch condition, you can rewrite the above example as:

Figure: Standard poll example

     prog envfrom
     do
       on stdpoll($1, ehlo_domain, mailfrom_address)
       do
       when success:
         accept
       when not_found or failure:
         reject 550 5.1.0 "Sender validity not confirmed"
       when temp_failure:
         tempfail 450 4.1.0 "Try again later"
       done
     done

As you see the statement is pretty similar to switch.  The major syntactic difference is the use of the keyword when to introduce conditional branches.

General syntax of the on statement is:

     on CONDITION
     do
       when X1 [or X2 ...]:
         STMT1
       when Y1 [or Y2 ...]:
         STMT2
         .
         .
         .
     done

The CONDITION is either a function call or a special poll statement (see below).  The values used in when branches are normally symbolic exception names (see exception names).

When the compiler processes the on statement it does the following:

 1. Builds a unique wrapper function, similar to that described in figure-poll-wrapper;  The name of the function is constructed from the CONDITION function name and an unsigned number, called exception mask, that is unique for each combination of exceptions used in when branches;  To avoid name clashes with the user-defined functions, the wrapper name begins and ends with $ which normally is not allowed in the identifiers;

 2. Translates the on body to the corresponding switch statement;

A special form of the CONDITION is poll keyword, whose syntax is:

     poll [for] EMAIL
          [host HOST]
          [from DOMAIN]
          [as EMAIL]

The order of particular keywords in the poll statement is arbitrary, for example as EMAIL can appear before EMAIL as well as after it.

The simplest form, poll EMAIL, performs the standard sender verification of email address EMAIL.  It is translated to the following function call:

       stdpoll(EMAIL, ehlo_domain, mailfrom_address)

The construct poll EMAIL host HOST, runs the strict sender verification of address EMAIL on the given host. It is translated to the following call:

       strictpoll(HOST, EMAIL, ehlo_domain, mailfrom_address)

Other keywords of the poll statement modify these two basic forms.  The as keyword introduces the email address to be used in the SMTP MAIL FROM command, instead of mailfrom_address.  The from keyword sets the domain name to be used in EHLO command.  So, for example the following construct:

       poll EMAIL host HOST from DOMAIN as ADDR

is translated to

       strictpoll(HOST, EMAIL, DOMAIN, ADDR)

To summarize the above, the code described in figure-stdpoll can be written as:

     prog envfrom
     do
       on poll $f do
       when success:
         accept
       when not_found or failure:
         reject 550 5.1.0 "Sender validity not confirmed"
       when temp_failure:
         tempfail 450 4.1.0 "Try again later"
       done
     done

Modules
=======

A module is a logically isolated part of code that implements a separate concern or feature and contains a collection of conceptually united functions and/or data.  Each module occupies a separate compilation unit (i.e. file).  The functionality provided by a module is incorporated into another module or the main program by requiring this module or by importing the desired components from it.

Declaring Modules
-----------------

A module file must begin with a module declaration:

     module MODNAME [INTERFACE-TYPE].

Note the final dot.

The MODNAME parameter declares the name of the module.  It is recommended that it be the same as the file name without the .mf extension.  The module name must be a valid MFL literal.  It also must not coincide with any defined MFL symbol, therefore we recommend to always quote it (see example below).

The optional parameter INTERFACE-TYPE defines the default scope of visibility for the symbols declared in this module.  If it is public, then all symbols declared in this module are made public (importable) by default, unless explicitly declared otherwise (see scope of visibility).  If it is static, then all symbols, not explicitly marked as public, become static.  If the INTERFACE-TYPE is not given, public is assumed.

The actual MFL code follows the module line.

The module definition is terminated by the logical end of its compilation unit, i.e. either by the end of file, or by the keyword bye, whichever occurs first.

Special keyword bye may be used to prematurely end the current compilation unit before the physical end of the containing file. Any material between bye and the end of file is ignored by the compiler.

Let's illustrate these concepts by writing a module revip:

     module 'revip' public.

     func revip(string ip)
       returns string
     do
       return inet_ntoa(ntohl(inet_aton(ip)))
     done

     bye

     This text is ignored.  You may put any additional
     documentation here.

Scope of Visibility
-------------------

Scope of Visibility of a symbol defines from where this symbol may be referred to.  Symbols in MFL may have either of the following two scopes:

Public
     Public symbols are visible from the current module, as well as from any external modules, including the main script file, provided that they are properly imported (see import).

Static
     Static symbols are visible only from the current module.  There is no way to refer to them from outside.

The default scope of visibility for all symbols declared within a module is defined in the module declaration (see module structure).  It may be overridden for any individual symbol by prefixing its declaration with an appropriate qualifier: either public or static.

Require and Import
------------------

Functions or variables declared in another module must be imported prior to their actual use.  MFL provides two ways of doing so: by requiring the entire module or by importing selected symbols from it.

 -- Module Import: require modname
     The require statement instructs the compiler to locate the module MODNAME and to load all public interfaces from it.

The compiler looks for the file MODNAME.mf in the current search path (see include search path).  If no such file is found, a compilation error is reported.

For example, the following statement:

     require revip

imports all interfaces from the module revip.mf.

Another, more sophisticated way to import from a module is to use the from ... import construct:

     from MODULE import SYMBOLS.

Note the final dot.  The from and module statements are the only two constructs in MFL that require the delimiter.

The MODULE has the same semantics as in the require construct.  The SYMBOLS is a comma-separated list of symbol names to import from MODULE.  A symbol name may be given in several forms:

 1. Literal

     Literals specify exact symbol names to import.  For example, the following statement imports from module A.mf symbols foo and bar:

          from A import foo,bar.

 2. Regular expression

     Regular expressions must be surrounded by slashes.  A regular expression instructs the compiler to import all symbols whose names match that expression.  For example, the following statement imports from A.mf all symbols whose names begin with foo and contain at least one digit after it:

          from A import '/^foo.*[0-9]/'.

     The type of regular expressions used in the from statement is controlled by #pragma regex (see regex).

 3. Regular expression with transformation

     Regular expression may be followed by a s-expression, i.e. a sed-like expression of the form:

          s/REGEXP/REPLACE/[FLAGS]

     where REGEXP is a regular expression, REPLACE is a replacement for each part of the input that matches REGEXP. S-expressions and their parts are discussed in detail in s-expression.

     The effect of such construct is to import all symbols that match the regular expression and apply the s-expression to their names.

     For example:

          from A import '/^foo.*[0-9]/s/.*/my_&/'.

     This statement imports all symbols whose names begin with foo and contain at least one digit after it, and renames them, by prefixing their names with the string my_.  Thus, if A.mf declared a function foo_1, it becomes visible under the name of my_foo_1.

MFL Preprocessor
================

Before compiling the script file, mailfromd preprocesses it.  The built-in preprocessor handles only file inclusion (see include), while the rest of traditional facilities, such as macro expansion, are supported via m4, which is used as an external preprocessor.

The detailed description of m4 facilities lies far beyond the scope of this document.  You will find a complete user manual in GNU M4 (GNU M4 macro processor).  For the rest of this section we assume the reader is sufficiently acquainted with m4 macro processor.

The external preprocessor is invoked with -s flag, instructing it to include line synchronization information in its output, which is subsequently used by MFL compiler for purposes of error reporting.  The initial set of macro definitions is supplied in file pp-setup, located in the library search path (It is
usually located in
/usr/local/share/mailfromd/VERSION/include/pp-setup.), which is fed to the preprocessor input before the script file itself. The default pp-setup file renames all m4 built-in macro names so they all start with the prefix m4_ (This is similar to GNU m4 --prefix-builtin options.  This approach was chosen to allow for using non-GNU m4 implementations as well.).  It changes comment characters to /*, */ pair, and leaves the default quoting characters, grave (`) and acute (') accents without change.  Finally, pp-setup defines the following macros:

 -- M4 Macro: boolean defined (IDENTIFIER)
     The IDENTIFIER must be the name of an optional abstract argument to the function.  This macro must be used only within a function definition.  It expands to the MFL expression that yields true if the actual parameter is supplied for IDENTIFIER. For example:

          func rcut(string text; number num)
            returns string
          do
            if (defined(num))
              return substr(text, length(text) - num)
            else
              return text
            fi
          done

     This function will return last NUM characters of TEXT if NUM is supplied, and entire TEXT otherwise, e.g.:

          rcut("text string") => "text string"
          rcut("text string", 3) => "ing"

     Invoking the defined macro with the name of a mandatory argument yields true

 -- M4 Macro: printf (FORMAT, ...)
     Provides a printf statement, that formats its optional parameters in accordance with FORMAT and sends the resulting string to the current log output (see Logging and Debugging). See String formatting, for a description of FORMAT.

     Example usage:

          printf('Function %s returned %d', funcname, retcode)

 -- M4 Macro: string _ (MSGID)
     A convenience macro.  Expands to a call to gettext (see NLS Functions).

 -- M4 Macro: string_list_iterate (LIST, DELIM, VAR, CODE)
     This macro intends to compensate for the lack of array data type in MFL.  It splits the string LIST into segments delimited by string DELIM.  For each segment, the MFL code CODE is executed.  The code can use the variable VAR to refer to the segment string.

     For example, the following fragment prints names of all existing directories listed in the PATH environment variable:

          string path getenv("PATH")
          string seg

          string_list_iterate(path, ":", seg, `
               if access(seg, F_OK)
                 echo "%seg exists"
               fi')

     Care should be taken to properly quote its arguments.  In the code below the string str is treated as a comma-separated list of values.  To avoid interpreting the comma as argument delimiter the second argument must be quoted:

          string_list_iterate(str, `","', seg, `
               echo "next segment: " . seg')

 -- M4 Macro: N_ (MSGID)
     A convenience macro, that expands to MSGID verbatim.  It is intended to mark the literal strings that should appear in the .po file, where actual call to gettext (see NLS Functions) cannot be used.  For example:

          /* Mark the variable for translation: cannot use gettext here */
          string message N_("Mail accepted")

          prog envfrom
          do
            ...
            /* Translate and log the message */
            echo gettext(message)

You can obtain the preprocessed output, without starting actual compilation, using -E command line option:

     $ mailfromd -E file.mf

The output is in the form of preprocessed source code, which is sent to the standard output.  This can be useful, among others, to debug your own macro definitions.

Macro definitions and deletions can be made on the command line, by using the -D and -U options.  They have the following format:

-D NAME[=VALUE]
--define=NAME[=VALUE]
     Define a symbol NAME to have a value VALUE.  If VALUE is not supplied, the value is taken to be the empty string.  The VALUE can be any string, and the macro can be defined to take arguments, just as if it was defined from within the input using the m4_define statement.

     For example, the following invocation defines symbol COMPAT to have a value 43:

          $ mailfromf -DCOMPAT=43

-U NAME

--undefine=NAME
     A counterpart of the -D option is the option -U (--undefine).  It undefines a preprocessor symbol whose name is given as its argument.  The following example undefines the symbol COMPAT:

          $ mailfromf -UCOMPAT

The following two options are supplied mainly for debugging purposes:

--no-preprocessor
     Disables the external preprocessor.

--preprocessor=COMMAND
     Use COMMAND as external preprocessor.  Be especially careful with this option, because mailfromd cannot verify whether COMMAND is actually some kind of a preprocessor or not.

Example of a Filter Script File
===============================

In this section we will discuss a working example of the filter script file.  For the ease of illustration, it is divided in several sections.  Each section is prefaced with a comment explaining its function.

This filter assumes that the mailfromd.conf file contains the following:

     relayed-domain-file (/etc/mail/sendmail.cw,
                          /etc/mail/relay-domains);
     io-timeout 33;
     database cache {
       negative-expire-interval 1 day;
       positive-expire-interval 2 weeks;
     };

Of course, the exact parameter settings may vary, what is important is that they be declared.  See Mailfromd Configuration, for a description of mailfromd configuration file syntax.

Now, let's return to the script.  Its first part defines the configuration settings for this host:

     #pragma regex +extended +icase

     set mailfrom_address "<>"
     set ehlo_domain "gnu.org.ua"

The second part loads the necessary source modules:

     require 'status'
     require 'dns'
     require 'rateok'

Next we define envfrom handler.  In the first two rules, it accepts all mails coming from the null address and from the machines which we relay:

     prog envfrom
     do
       if $f = ""
         accept
       elif relayed hostname($client_addr)
         accept
       elif hostname($client_addr) = $client_addr
         reject 550 5.7.7 "IP address does not resolve"

Next rule rejects all messages coming from hosts with dynamic IP addresses.  A regular expression used to catch such hosts is not 100% fail-proof, but it tries to cover most existing host naming patterns:

        elif hostname($client_addr) matches
              ".*(adsl|sdsl|hdsl|ldsl|xdsl|dialin|dialup|\
     ppp|dhcp|dynamic|[-.]cpe[-.]).*"
          reject 550 5.7.1 "Use your SMTP relay"

Messages coming from the machines whose host names contain something similar to an IP are subject to strict checking:

        elif hostname($client_addr) matches
        ".*[0-9]{1,3}[-.][0-9]{1,3}[-.][0-9]{1,3}[-.][0-9]{1,3}.*"
          on poll host $client_addr for $f do
          when success:
            pass
          when not_found or failure:
            reject 550 5.1.0 "Sender validity not confirmed"
          when temp_failure:
            tempfail
          done

If the sender domain is relayed by any of the yahoo.com or nameserver.com MXs, no checks are performed.  We will greylist this message in envrcpt handler:

        elif $f mx fnmatches "*.yahoo.com"
             or $f mx fnmatches "*.namaeserver.com"
          pass

Finally, if the message does not meet any of the above conditions, it is verified by the standard procedure:

        else
          on poll $f do
          when success:
            pass
          when not_found or failure:
            reject 550 5.1.0 "Sender validity not confirmed"
          when temp_failure:
            tempfail
          done
        fi

At the end of the handler we check if the sender-client pair does not exceed allowed mail sending rate:

        if not rateok("$f-$client_addr", interval("1 hour 30 minutes"), 100)
          tempfail 450 4.7.0 "Mail sending rate exceeded.  Try again later"
        fi
     done

Next part defines the envrcpt handler.  Its primary purpose is to greylist messages from some domains that could not be checked otherwise:

     prog envrcpt
     do
       set gltime 300
       if $f mx fnmatches "*.yahoo.com"
          or $f mx fnmatches "*.namaeserver.com"
          and not dbmap("/var/run/whitelist.db", $client_addr)
         if greylist("$client_addr-$f-$rcpt_addr", gltime)
           if greylist_seconds_left = gltime
             tempfail 450 4.7.0
                    "You are greylisted for %gltime seconds"
           else
             tempfail 450 4.7.0
                    "Still greylisted for " .
                    %greylist_seconds_left . " seconds"
           fi
         fi
       fi
     done

Reserved Words
==============

For your reference, here is an alphabetical list of all reserved words:

  * __defpreproc__

  * __defstatedir__

  * __file__

  * __function__

  * __line__

  * __major__

  * __minor__

  * __module__

  * __package__

  * __patch__

  * __preproc__

  * __statedir__

  * __version__

  * accept

  * add

  * and

  * alias

  * begin

  * break

  * bye

  * case

  * catch

  * const

  * continue

  * default

  * delete

  * discard

  * do

  * done

  * echo

  * end

  * elif

  * else

  * fi

  * fnmatches

  * for

  * from

  * func

  * if

  * import

  * loop

  * matches

  * module

  * next

  * not

  * number

  * on

  * or

  * pass

  * precious

  * prog

  * public

  * reject

  * replace

  * return

  * returns

  * require

  * set

  * static

  * string

  * switch

  * tempfail

  * throw

  * try

  * vaptr

  * when

  * while

Several keywords are context-dependent: mx is a keyword if it appears before matches or fnmatches.  Following strings are keywords in on context:

  * as

  * host

  * poll

The following keywords are preprocessor macros:

  * defined

  * _ (an underscore)

  * N_

Any keyword beginning with a m4_ prefix is a reserved preprocessor symbol.

The MFL Library Functions
*************************

     [file functions.texi not included]

Using the GNU Emacs MFL Mode
****************************

MFL sources are usual ASCII files and you may edit them with any editor you like.  However, the best choice for this job (as well as for many others) is, without doubt, GNU Emacs.  To ease the work of editing script files, the mailfromd package provides a special Emacs mode, called MFL mode.

The elisp source file providing this mode, mfl-mode.el, is installed automatically, provided that GNU Emacs is present on your machine.  To enable the mode, add the following lines to your Emacs setup file (either system-wide site-start.el, or your personal one, ~/.emacs):

     (autoload 'mfl-mode "mfl-mode")
     (setq auto-mode-alist (append auto-mode-alist
                            '(("/etc/mailfromd.mf" . mfl-mode)
                              ("\\.mf$" . mfl-mode))))

The first directive loads the MFL mode, and the second one tells Emacs to apply it to any file whose name ends in /etc/mailfromd.mf (This will match most existing installations.  In the unlikely case that your $sysconfdir does not end in /etc, you will have to edit the directive accordingly.) or in a .mf suffix.

MFL mode provides automatic indentation and syntax highlighting for MFL sources.  The default indentation setup is the same as the one used throughout this book:

  * Handler and function definitions start at column 1;

  * A block statement, i.e. do, done, if, else, elif and fi, occupies a line by itself, with the only exception that do after an on statement is located on the same line with it;

  * A do statement that follows function or handler definition is placed in column 1.

  * Each subsequent level of nesting is indented two columns to the right (see mfl-basic-offset).

  * A closing statement (done, else, elif, fi) is placed at the same column as the corresponding opening statement;

  * Branch statements (case and when) are placed in the same column as their controlling keyword (switch and on, correspondingly (see mfl-case-line-offset).

  * Loop substatements (see Loops) are offset 5 columns to the right from the controlling loop keyword. (see mfl-loop-statement-offset).  Continuation statements within loop header are offset 5 columns from the indentation of their controlling keyword, either for or while (see mfl-loop-continuation-offset).

The mode provides two special commands that help navigate through the complex filter scripts:

C-M-a
     Move to the beginning of current function or handler definition.

C-M-e
     Move to the end of current function or handler definition.

Here, current function or handler means the one within which your cursor currently stays.

You can use C-M-e repeatedly to walk through all function and handler definitions in your script files.  Similarly, repeatedly pressing C-M-a will visit all the definitions in the opposite direction (from the last up to the very first one).

Another special command, C-c C-c, allows to verify the syntax of your script file.  This command runs mailfromd in syntax check mode (see Testing Filter Scripts) and displays its output in a secondary window, which allows to navigate through eventual diagnostic messages and to jump to source locations described by them.

All MFL mode settings are customizable.  To change any of them, press M-x customize and visit Environment/Unix/Mfl customization group.  This group offers two subgroups: Mfl Lint group and Mfl Indentation group.

Mfl Lint group controls invocation of mailfromd by C-c C-c.  This group contains two variables:

 -- MFL-mode setting: mfl-mailfromd-command
     The mailfromd to be invoked.  By default, it is mailfromd.  You will have to change it, if mailfromd cannot be found using PATH environment variable, or if you wish to pass it some special options.  However, do not include --lint or -I options in this variable.  The --lint option is given automatically, and include paths are controlled by mfl-include-path variable (see below).

 -- MFL-mode setting: mfl-include-path
     A list of directories to be appended to mailfromd include search path (see include search path).  By default it is empty.

Mfl Indentation group controls automatic indentation of MFL scripts.  This group contains the following settings:

 -- MFL-mode setting: mfl-basic-offset
     This variable sets the basic indentation increment.  It is set to 2, by default, which corresponds to the following indentation style:

          prog envfrom
          do
            if $f = ""
              accept
            else
              ...
            fi
          done

 -- MFL-mode setting: mfl-case-line-offset
     Indentation offset for case and when lines, relative to the column of their controlling keyword.  The default is 0, i.e.:

          switch x
          do
          case 0:
            ...
          default:
            ...
          done

 -- MFL-mode setting: mfl-returns-offset
     Indentation offset of returns and alias statements, relative to the controlling func keyword.  The default value is 2, which corresponds to:

          func foo()
            alias bar
            returns string

 -- MFL-mode setting: mfl-comment-offset
     Indentation increment for multi-line comments.  The default value is 1, which makes:

             /* first comment line
                second comment line */

 -- MFL-mode setting: mfl-loop-statement-offset
     Indentation increment for parts of a loop statement.  The default value is 5, which corresponds to the following style:

          loop for STMT,
               while COND,
               INCR
          do

 -- MFL-mode setting: mfl-loop-continuation-offset
     If any of the loop parts occupies several lines, the indentation of continuation lines relative to the first line is controlled by mfl-loop-continuation-offset, which defaults to 5:

          loop for set n 0
                    set z 1,
               while n != 10
                    or z != 2,
               set n n + 1

Configuring mailfromd
*********************

Upon startup, mailfromd checks if the file /etc/mailfromd.conf exists. (The exact location is determined at compile time: the /etc directory is the system configuration directory set when building mailfromd (see Building).)  If it does, the program attempts to retrieve its configuration settings from that file.

The mailfromd.conf file must be written in the GNU mailutils configuration format, as described in Configuration File Syntax (GNU Mailutils Manual).  This format can be summarized as follows:

Comments
     Inline comments begin with // or # and end at the end of the line.  Multiline comments are delimited by /* and */.  Multiline comments cannot be nested, but can contain inline comment markers.

Empty lines and whitespace
     Empty lines are ignored.  Whitespace characters (i.e. horizontal, vertical space, and newline) are ignored, except as they serve to separate tokens.

Statements
     A statement consists of a keyword and a value, separated by whitespace.  Statements terminate with a semicolon.  E.g.

          pidfile /var/run/mailfromd.pid;

Block statements
     A block statement consists of a keyword and a list of statements enclosed in { and } characters.  Optional label can appear between the keyword and opening curly brace.  E.g.:

          logging {
            syslog on;
            facility mail;
          }

     Block statement is not required to terminate with a semicolon, although it is allowed to.

File Inclusion
     The include statement causes inclusion of the file listed as its value:

          include /usr/share/mailfromd/config.inc;

The mailfromd.conf file is used by all programs that form the mailfromd package, i.e.  mailfromd, calloutd, mfdbtool, and pmult.  Since the sets of statements understood by each of them differ, special syntactic means are provided to separate program-specific configurations from each other.

First of all, if the argument to include is a directory, then the program will search that directory for a file with the same name as the base name of the program itself.  If found, this file will be loaded after finishing parsing the mailfromd.conf file. Otherwise, this statement is ignored.

Secondly, the special block statement program TAG is processed only if TAG matches the base name of the program being run.  Again, it is processed after the main mailfromd.conf file.

Thus, if you need to provide configuration for the calloutd component, there are two ways of doing so.  First, you can place it to a file named calloutd placed in a separate directory (say, /etc/mailfromd.d), and use the name of that directory in a include statement in the main configuration file:

     include /etc/mailfromd.d;

Secondly, you can use the program statement as follows:

     program calloutd {
       ...
     }

Special Configuration Data Types
================================

In addition to the usual data types (see Statements (GNU Mailutils Manual)), mailfromd configuration introduces the following two special ones:

time interval specification
     The time interval specification is a string that defines an interval, much the same way we do this in English: it consists of one or more pairs number-time unit.  For example, the following are valid interval specifications:

          1 hour
          2 hours 35 seconds
          1 year 7 months 2 weeks 2 days 11 hours 12 seconds

     The pairs can occur in any order, however unusual it may sound to a human ear, e.g. 2 days 1 year.  If the time unit is omitted, seconds are supposed.

Connection URL

     unix://FILE
     unix:FILE
     local://FILE
     local:FILE
          A named pipe (socket).

     inet://ADDRESS:PORT
     inet:PORT@ADDRESS
          An IPv4 connection to host ADDRESS at port PORT.  Port must be specified either as a decimal number or as a string representing the port name in /etc/services.

     inet6:PORT@ADDRESS
          An IPv6 connection to host ADDRESS at port PORT.  This port type is not yet supported.

Base Mailfromd Configuration
============================

 -- Mailfromd Conf: script-file file
     Read filter script from FILE.  By default it is read from SYSCONFDIR/mailfromd.mf.

 -- Mailfromd Conf: setvar name value
     Initialize MFL variable NAME to VALUE.

 -- Mailfromd Conf: include-path path
     Add directories to the list of directories to be searched for header files.  See include search path.

     Argument is a list of directory names separated by colons.

 -- Mailfromd Conf: state-directory dir
     Set program state directory.  See statedir.

 -- Mailfromd Conf: relayed-domain-file file
     Append domain names from the named FILE to the list of relayed domains.  This list can be inspected from MFL script using the relayed function (see relayed).

     The FILE argument is either a single file name or a list of file names, e.g.:

          relayed-domain-file /etc/mail/sendmail.cw;
          relayed-domain-file (/etc/mail/sendmail.cw, /etc/mail/relay-domains);

 -- Mailfromd Conf: source-ip ipaddr
     Set source IP address for outgoing TCP connections.

 -- Mailfromd Conf: pidfile file
     Set the name of the file to store PID value in.  The file must be writable for the user or group mailfromd runs as (see conf-priv).

Server Configuration
====================

A single mailfromd daemon can run several servers. These are configured in the following statement:

     server TYPE {
       id NAME;
       listen URL;
       backlog NUM;
       max-instances NUM;
       single-process BOOL;
       reuseaddr BOOL;
       option LIST;
       default BOOL;
       callout URL;
       acl { ... }
     }

 -- Mailfromd Conf: server TYPE
     Define a server.  The TYPE is either milter or callout.  See SMTP Timeouts, for a description of various types of servers.

     The substatements in the server block provide parameters for configuring this server.

 -- server: id name
     Assign an identifier to this server.  This identifier is used as a suffix to syslog tag (see syslog tag) in messages related to this server.  For example, if a server block had the following statement in it:

          id main;

     then all messages related to this server will be marked with tag mailfromd#main.

     The part before the # is set using the tag statement in logging block (see Mailutils Configuration File (GNU Mailutils Manual)).

 -- server: listen url
     Listen for connections on the given URL. See milter port specification, for a description of allowed URL formats.

     Example:

          listen inet://10.10.10.1:3331;

 -- server: backlog NUM
     Configures the size of the queue of pending connections.  Default value is 8.

 -- server: max-instances number
     Sets the maximum number of instances allowed for this server.

 -- server: single-process bool
     When set to yes, this server will run in single-process mode, i.e. it will not fork sub-processes to serve requests.  This option is meant exclusively to assist in debugging mailfromd.  Don't use it for anything else but for debugging!

 -- server: reuseaddr bool
     When set to yes, mailfromd will attempt to reuse existing socket addresses.  This is the default behavior.

If the server TYPE is callout, the following statement is also allowed:

 -- server: option LIST
     Configures server options.  As of version VERSION only one option is defined:

     default
          Mark this server as the default one.  This means it will be used by every milter server that doesn't define the callout-url statement.

 -- server: default bool
     When set to yes, this server is marked as a default callout server for all milter servers declared in the configuration.  This is equivalent to option default.

if the server TYPE is milter, you can use the following statement to query a remote callout server:

 -- server: callout url
     Use a callout server at URL (see milter port specification).

You can also set a global callout server, which will be used by all milter servers that do not set the callout statement:

 -- Mailfromd Conf: callout-url url
     Set global callout server.  See milter port specification, for allowed URL formats.

Milter Connection Configuration
===============================

 -- Mailfromd Conf: milter-timeout time
     Sets the timeout value for connection between the filter and the MTA.  Default value is GACOPYZ_TIMEOUT seconds.  You normally do not need to change this value.

 -- Mailfromd Conf: acl
     This block statement configures access control list for incoming Milter connections.  See Mailutils Configuration File (GNU Mailutils Manual), for a description of its syntax.  E.g.:

          acl {
            allow from 10.10.10.0/24;
            deny from any;
          }

Logging and Debugging configuration
===================================

 -- Mailfromd Conf: logger mech
     Set default logger mechanism.  Allowed values for MECH are:

     stderr
          Log everything to the standard error.

     syslog
          Log to syslog.

     syslog:async
          Log to syslog using the asynchronous syslog implementation.

     See Logging and Debugging, for a detailed discussion. See also Using non-blocking syslog, for information on how to set default syslog implementation at compile time.

 -- Mailfromd Conf: debug spec
     Set mailfromd debug verbosity level.  The SPEC must be a valid debugging level specification (see debugging level specification).

 -- Mailfromd Conf: stack-trace bool
     Enables stack trace dumps on runtime errors.  This feature is useful for locating the source of an error, especially in complex scripts.  See tracing runtime errors, for a detailed description.

 -- Mailfromd Conf: trace-actions bool
     Enable action tracing.  If BOOL is true, mailfromd will log all executed actions.  See Logging and Debugging, for a detailed description of action tracing.

 -- Mailfromd Conf: trace-program modlist
     Enable program instruction tracing for modules in MODLIST, a comma-separated list of source code modules, e.g.:

          trace-program (bi_io,bi_db);

     This statement enables tracing for functions from modules bi_io.c and bi_db.c (notice, that you need not give file suffixes).

     This tracing is useful for debugging mailfromd, but is not advised to use otherwise, since it is very time-costly.

 -- Mailfromd Conf: transcript bool
     Enable transcripts of call-out SMTP sessions. See SMTP transcript, for a detailed description of SMTP transcripts.

Timeout Configuration
=====================

The SMTP timeouts used in callout sessions are configured via smtp-timeout statement:

Syntax
------

     smtp-timeout TYPE {
       connection INTERVAL;
       initial-response INTERVAL;
       helo INTERVAL;
       mail INTERVAL;
       rcpt INTERVAL;
       rset INTERVAL;
       quit INTERVAL;
     }

 -- Mailfromd Conf: smtp-timeout TYPE
     Declare SMTP timeouts of the given TYPE, which may be soft or hard.

     Callout SMTP sessions initiated by polling functions, are controlled by two sets of timeouts: soft and hard. Soft timeouts are used by the mailfromd milter servers.  Hard timeouts are used by callout servers (see callout server). When a soft timeout is exceeded, the calling procedure is delivered an e_temp_failure exception and the session is scheduled for processing by a callout server.  The latter re-runs the session using hard timeouts.  If a hard timeout is exceeded, the address is marked as not_found and is stored in the cache database with that status.

     Normally, soft timeouts are set to shorter values, suitable for use in MFL scripts without causing excessive delays.  Hard timeouts are set to large values, as requested by RFC 2822 and guarantee obtaining a definite answer (see below for the default values).

Statements
----------

The TIME argument for all smtp-timeout sub-statements is expressed in time interval units, as described in time interval specification.

 -- smtp-timeout: connection time
     Sets initial connection timeout for callout tests.  If the connection is not established within this time, the corresponding callout function returns temporary failure.

 -- smtp-timeout: initial-response time
     Sets the time to wait for the initial SMTP response.

 -- smtp-timeout: helo time
     Timeout for a response to HELO (or EHLO) command.

 -- smtp-timeout: mail time
     Timeout for a response to MAIL command.

 -- smtp-timeout: rcpt time
     Timeout for a response to RCPT command.

 -- smtp-timeout: rset time
     Timeout for a response to RSET command.

 -- smtp-timeout: quit time
     Timeout for a response to QUIT command.

Default Values
--------------

The default timeout settings are:

Table: Default SMTP timeouts

Timeout        Soft   Hard
connection          10s   5m
initial-response    30s   5m
helo                I/O   5m
mail                I/O   10m
rcpt                I/O   5m
rset                I/O   5m
quit                I/O   2m

 -- Mailfromd Conf: io-timeout time
     Sets a general SMTP I/O operation timeout.  This timeout is used as the default for entries marked with I/O in the above table.  The default is 3 seconds.

Call-out Configuration
======================

 -- Mailfromd Conf: ehlo-domain string
     Sets default domain used in EHLO (or HELO) SMTP command when probing the remote host.  This value can be overridden by from parameter to poll command (see poll).

     This statement assigns the value STRING to the ehlo_domain variable (see ehlo_domain), and is therefore equivalent to

          setvar ehlo_domain STRING;

 -- Mailfromd Conf: mail-from-address string
     Sets default email addresses used in MAIL FROM: SMTP command when probing the remote host.  This value can be overridden by as parameter to poll command (see poll).

     This statement assigns the value STRING to the mailfrom_address variable (see mailfrom_address), and is therefore equivalent to

          setvar mailfrom_address STRING;

 -- Mailfromd Conf: enable-vrfy bool
     Enables the use of SMTP VRFY statement prior to normal callout sequence.  If VRFY is supported by the remote server, mailfromd relies on its reply and does not perform normal callout.

     The use of this statement is not recommended, because many existing VRFY implementations always return affirmative result, no matter is the requested email handled by the server or not.

     The default is enable-vrfy no, i.e. VRFY is disabled.

Privilege Configuration
=======================

 -- Mailfromd Conf: user name
     Switch to this user's privileges after startup. See Starting and Stopping, for a discussion of the privileges mailfromd runs under and the options that affect them.  See also group below.

 -- Mailfromd Conf: group name
     Retain the supplementary group NAME when switching to user privileges.  By default mailfromd clears the list of supplementary groups when switching to user privileges, but this statement allows to retain the given group.  It can be specified multiple times to retain several groups.  This option may be necessary to maintain proper access rights for various files.  See Starting and Stopping.

Database Configuration
======================

Syntax
------

     database DBNAME {
       file NAME;
       enable BOOL;
       expire-interval INTERVAL;
       positive-expire-interval INTERVAL;
       negative-expire-interval INTERVAL;
     }

 -- Mailfromd Conf: database dbname
     The database statement controls run-time parameters of a DBM database identified by DBNAME.  Allowed values for the latter are: cache, rate and greylist for main cache, DNS lookup, sending rate and greylisting databases, correspondingly.

Statements
----------

 -- database: file name
     Set the database file name.

 -- database: enable bool
     Enable or disable this database.

 -- database: expire-interval time
     Set the expiration interval for this database DBNAME. See time interval specification, for a description of TIME format.

 -- database: positive-expire-interval time
     This statement is valid only for cache database.  It sets the expiration interval for positive (success) cache entries.

 -- database: negative-expire-interval time
     This statement is valid only for cache database, where it sets expiration interval for negative (not_found) cache entries.

Additional Statements
---------------------

 -- Mailfromd Conf: database-type TYPE
     Set default database type.  TYPE is one of the database types supported by mailutils (i.e., for Mailutils 3.0: gdbm, ndbm, bdb, kc, and tc).  Run

          mailfromd --show-defaults | grep 'supported databases:'

     to get a list of type names supported by your build of mailfromd.

 -- Mailfromd Conf: database-mode MODE
     Defines file mode for newly created database files.  MODE must be a valid file mode in octal.

 -- Mailfromd Conf: lock-retry-count number
     Set maximum number of attempts to acquire the lock.  The time between each two successive attempts is given by lock-retry-timeout statement (see below).  After the NUMBER of failed attempts, mailfromd gives up.

 -- Mailfromd Conf: lock-retry-timeout time
     Set the time span between the two locking attempts.  Any valid time interval specification (see time interval specification) is allowed as argument.

Runtime Constants Configuration
===============================

 -- Mailfromd Conf: runtime { statements }
     The statements in the runtime section configure various values used by MFL builtin functions.

 -- runtime: max-streams number
     Sets the maximum number of stream descriptors that can be opened simultaneously.  Default is MAX_IOSTREAMS.  See I/O functions.

 -- runtime: max-open-mailboxes number
     Sets the maximum number of available mailbox descriptors.  This value is used by MFL mailbox functions (see Mailbox functions).

 -- runtime: max-open-messages number
     Sets the maximum number of messages that can be opened simultaneously using the mailbox_get_message function.  See Message functions, for details.

Standard Mailutils Statements
=============================

The following standard Mailutils statements are understood:

Statement   Reference
auth   see Mailutils Configuration File (GNU Mailutils Manual).
debug   see Mailutils Configuration File (GNU Mailutils Manual).
include   see Mailutils Configuration File (GNU Mailutils Manual).
logging   see Mailutils Configuration File (GNU Mailutils Manual).
mailer   see Mailutils Configuration File (GNU Mailutils Manual).
locking   see Mailutils Configuration File (GNU Mailutils Manual).

Mailfromd Command Line Syntax
*****************************

The mailfromd binary is started from the command line using the following syntax (brackets indicate optional parts):

     $ mailfromd [OPTIONS] [ASGN] [SCRIPT]

The meaning of each invocation part is described in the table below:

options
     The command line options (see options).

asgn
     Sendmail macro assignments.  These are currently meaningful only with the --test option (see test mode), but this may change in the future.  Each assignment has the form:

          VAR=VALUE

     where VAR is the name of a Sendmail macro and VALUE is the value to be assigned to it.

script
     The file name of the filter script, if other than the default one.

Command Line Options.
=====================

Operation Modifiers
-------------------

     daemon, mailfromd

--daemon
     Run in daemon mode (default).

     run, mailfromd

--run[=START]
     Load the script named in the command line and execute the function named START, or main, if START is not given. See Run Mode, for a detailed description of this feature.

     show-defaults, mailfromd

--show-defaults
     Show compilation defaults.  See Databases.

     test, mailfromd

-t[STATE]
--test[=STATE]
     Run in test mode.  See Testing Filter Scripts.  Default STATE is envfrom.  This option implies --stderr (see --stderr).

General Settings
----------------

     callout-socket, mailfromd

--callout-socket=STRING
     Set socket for the default callout server. This is mainly useful together with the --mtasim option.

     foreground, mailfromd

--foreground
     Stay in foreground.  When given this option, mailfromd will not disconnect itself from the controlling terminal and will run in the foreground.

     group, mailfromd

-g NAME
--group=NAME

     Retain the group NAME when switching to user privileges.  See Starting and Stopping.

     This option complements the group configuration statement (see group).

     include, mailfromd

--include=DIR
-I DIR
     Add the directory DIR to the list of directories to be searched for header files.  This will affect the functioning of #include statement.  See include, for a discussion of file inclusion.

     mailer, mailfromd

--mailer=URL
-M URL
     Set the URL of the mailer to use.  See Mail Sending Functions.

     mtasim, mailfromd

--mtasim
     This option is reserved for use by mtasim (see mtasim).

     optimize, mailfromd

-O[LEVEL]
--optimize[=LEVEL]
     Set optimization level for code generator.  Two levels are implemented: 0, meaning no optimization, and 1, meaning full optimization.

     port, mailfromd milter-socket, mailfromd

-p STRING
--port=STRING
--milter-socket=STRING
     Set communication socket.  Overrides the listen configuration statement, which you are advised to use instead (see listen).

     pidfile, mailfromd

--pidfile=FILE
     Set pidfile name.  Overrides the pidfile configuration statement, which you are advised to use instead (see pidfile).

     relayed-domain-file, mailfromd

--relayed-domain-file=FILE
     Read relayed domains from FILE.  Overrides the relayed-domain-file configuration statement (see relayed-domain-file), which you are advised to use instead. See Avoiding Verification Loops, and the description of relayed function (see relayed) for more information.

     resolv-conf-file, mailfromd

--resolv-conf-file=FILE
     Read resolver settings from FILE, instead of the default /etc/resolv.conf.

     state-directory, mailfromd

--state-directory=DIR
     Set new program state directory.  See Local state directory, for the description of this directory and its purposes.  This option overrides the settings of state-directory configuration statement, described in state-directory.

     source-ip, mailfromd

-S IP
--source-ip=IP
     Set source address for TCP connections.  Overrides the source-ip configuration statement, which you are advised to use instead (see source-ip).

     user, mailfromd

-u NAME
--user NAME
     Switch to this user privileges after startup.  Overrides the user configuration file statement, which you are advised to use instead (see user).  Default user is DEFAULT_USER.

     variable, mailfromd

-v VAR=VALUE
--variable VAR=VALUE
     Assign VALUE to the global variable VAR.  The variable must be declared in your startup script.  See overriding initial values, for a detailed discussion of this option.

Preprocessor Options
--------------------

Following command line options control the preprocessor feature.  See Preprocessor, for a detailed discussion of these.

     no-preprocessor, mailfromd

--no-preprocessor
     Do not run the preprocessor.

     preprocessor, mailfromd

--preprocessor=COMMAND
     Use COMMAND as the external preprocessor instead of the default m4.

     define, mailfromd

-D NAME[=VALUE]
--define=NAME[=VALUE]
     Define a preprocessor symbol NAME to have a value VALUE.

     undefine, mailfromd

-U NAME
--undefine=NAME
     Undefine the preprocessor symbol NAME.

-E
     Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output.

Timeout Control
---------------

See time interval specification, for information on INTERVAL format.

     milter-timeout, mailfromd

--milter-timeout=INTERVAL
     Set MTA connection timeout.  Overrides milter-timeout statement in the mailfromd configuration file, which you are advised to use instead (see milter-timeout).

Logging and Debugging Options
-----------------------------

     location-column, mailfromd

--location-column
--no-location-column
     Mention column number in error messages.  See location-column.  Use --no-location-column to disable

     debug, mailfromd

-d STRING
--debug=STRING
     Set debugging level.  See Logging and Debugging.

     dump-code, mailfromd

--dump-code
     Parse and compile the script file and dump the disassembled listing of the produced code to the terminal.  See Logging and Debugging.

     dump-grammar-trace, mailfromd

--dump-grammar-trace
     Enable debugging the script file parser.  While parsing the file, the detailed dump of the parser states and tokens seen will be output.

     dump-lex-trace, mailfromd

--dump-lex-trace
     Enable debugging the lexical analyzer.  While parsing the script file, the detailed dump of the lexer states and matched rules will be output.

     dump-macros, mailfromd

--dump-macros
     Show Sendmail macros used in the script file.  The macro names are displayed as comma-separated lists, grouped by handler names. See Sendmail, for a detailed description of this option and its usage.

     dump-tree, mailfromd

--dump-tree
     Parse and compile the script file and dump the parse tree in a printable form to the terminal.

     dump-xref, mailfromd

--dump-xref
     Print a cross-reference of variables used in the filter script. See Testing Filter Scripts.

-E
     Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output.  See Preprocessor.

     lint, mailfromd

--lint
     Check script file syntax and exit.  If the file is OK, return 0 to the shell, otherwise print appropriate messages to stderr and exit with code 78 (configuration error).

     single-process, mailfromd

--single-process
     Do not fork sub-processes to serve requests.  This option is meant to assist in debugging mailfromd.  Don't use it for anything else but for debugging, as it terribly degrades performance!

     stack-trace, mailfromd

--stack-trace
--no-stack-trace
     Add MFL stack trace information to runtime error output. Overrides stack-trace configuration statement.  Use the --no-stack-trace to disable trace information.

     See tracing runtime errors, for more information on this feature.

     gacopyz-log, mailfromd

--gacopyz-log=LEVEL
     Set desired logging level for gacopyz library (see Gacopyz).  There are five logging levels.  The following table lists them in order of decreasing priority:

     fatal
          Log fatal errors.

     err
          Log error messages.

     warn
          Log warning messages.

     info
          Log informational messages.  In particular, this enables printing messages on each subprocess startup and termination, which look like that:

               Apr 28 09:00:11 host mailfromd[9411]: connect
                   from 192.168.10.1:50398
               Apr 28 09:00:11 host mailfromd[9411]: finishing
                   connection

          This level can be useful for debugging your scripts.

     debug
          Log debugging information.

     proto
          Log Milter protocol interactions.  This level prints huge amounts of information, in particular it displays dumps of each Milter packet sent and received.

     Although it is possible to set these levels independently of each other, it is seldom practical.  Therefore, the option --gacopyz-log=LEVEL enables all logging levels from LEVEL up.  For example, --gacopyz-log=warn enables log levels warn, err and fatal.  It is the default.  If you need to trace each subprocess startup and shutdown, set --gacopyz-log=info.  Setting the logging level to proto can be needed only for Gacopyz developers, to debug the protocol.

     See Testing Filter Scripts.

     logger, mailfromd

--logger=MECH
     Set logger mechanism (MECH is one of stderr, syslog, syslog:async).  See Logging and Debugging.

     log-facility, mailfromd

--log-facility=FACILITY
     Output logs to syslog FACILITY.

     log-tag, mailfromd

--log-tag=STRING
     Tag syslog entries with the given STRING, instead of the program name.

     source-info, mailfromd

--source-info
--no-source-info
     Include C source information in debugging messages.  This is similar to setting line-info yes in the debug configuration block (see line-info (GNU Mailutils Manual)).

     The --no-source-info can be used to cancel the effect of the line-info yes configuration statement.

     You do not need this option, unless you are developing or debugging mailfromd.

     syntax-check, mailfromd

--syntax-check
     Synonym for --lint.

     trace, mailfromd

--trace

--no-trace
     Enable or disable action tracing.  If --trace is given, mailfromd will log all executed actions.  See Logging and Debugging.

     trace-program, mailfromd

--trace-program[=STRING]
     Enable program instruction tracing.  With this option mailfromd will log execution of every instruction in the compiled filter program.  The optional arguments allows to specify a comma-separated list of source code modules for which the tracing is to be enabled, for example --trace-program=bi_io,bi_db enables tracing for functions from modules bi_io.c and bi_db.c (notice, that you need not give file suffixes in STRING).

     This option is useful for debugging mailfromd, but is not advised to use otherwise, since it is very time-costly.

     transcript, mailfromd

-X
--transcript
--no-transcript
     Enable or disable transcript of the SMTP sessions to the log channel.  See Logging and Debugging.

     syslog, mailfromd

--syslog
     Selects default syslog mechanism for diagnostic output.

     stderr, mailfromd

--stderr
     Directs all logging to standard output.  Similar to --logger=stderr.

     xref, mailfromd

--xref
     Same as --dump-xref.  See Logging and Debugging.

Informational Options
---------------------

-?
--help
     Give a short help summary.

--usage
     Give a short usage message.

-V
--version
     Print program version.

Starting and Stopping
=====================

Right after startup, when mailfromd has done the operations that require root privileges, it switches to the privileges of the user it is configured to run as (see default user privileges) or the one given in its configuration file (see user).  During this process it will drop all supplementary groups and switch to the principal group of that user.

Such limited privileges of the daemon can cause difficulties if your filter script needs to access some files (e.g. Sendmail databases) that are not accessible to that user and group.  For example, the following fragment using dbmap function:

     if dbmap("/etc/mail/aliases.db", $f, 1)
       ...
     fi

will normally fail, because /etc/mail/aliases.db is readable only to the root and members of the group smmsp.

In such situations you need to instruct mailfromd to retain the privileges of one or several supplementary groups when switching to the user privileges.  This is done using group statement in the mailfromd configuration file (see group).  In example above, you need to use the following settings:

     group smmsp;

(The same effect can be achieved with --group command line option: mailfromd --group=smmsp).

To stop a running instance of mailfromd use one of the following signals: SIGQUIT, SIGTERM, SIGINT. All three signals have the same effect: the program cancels handling any pending requests, uninitializes the communication socket (if it is a UNIX socket, the program unlinks it) and exits.

To restart the running mailfromd instance, send it SIGHUP.  For restart to be possible, two conditions must be met: mailfromd must be invoked with the full file name, and the configuration file name must be full as well.  If either of them is not met, mailfromd displays a similar warning message:

     warning: script file is given without full file name
     warning: restart (SIGHUP) will not work

or:

     warning: mailfromd started without full file name
     warning: restart (SIGHUP) will not work

The reaction of mailfromd on SIGHUP in this case is the same as on the three signals described previously, i.e. cleanup and exit immediately.

The PID of the master instance of mailfromd is kept on the pidfile, which is named mailfromd.pid and is located in the program state directory.  Assuming the default location of the latter, the following command will stop the running instance of the daemon:

     kill -TERM `head -n1 /usr/local/var/mailfromd/mailfromd.pid`

The default pidfile location is shown in the output of mailfromd --show-defaults (see Databases), and can be changed at run time using pidfile statement (see pidfile).

To facilitate the use of mailfromd, it is shipped with a shell script that can be used to launch it on system startup and shut it down when the system goes down.  The script, called rc.mailfromd, is located in the directory /etc of the distribution.  It takes a single argument, specifying the action that should be taken:

start
     Start the program.

stop
     Shut down the program

reload
     Reload the program, by sending it SIGHUP signal.

restart
     Shut down the program and start it again.

status
     Display program status.  It displays the PID of the master process and its command line, for example:

          $ /etc/rc.d/rc.mailfromd status
          mailformd appears to be running at 26030
          26030 /usr/local/sbin/mailfromd --group smmsp

     If the second line is not displayed, this most probably mean that there is a stale pidfile, i.e. the one left though the program is not running.

     An empty rc.mailfromd status output means that mailfromd is not running.

configtest [FILE]
     Check the script file syntax, report any errors found and exit.  If FILE is given it is checked instead of the default one.

macros [-c] [FILE]
     Parse the script file (or FILE, if it is given, extract the names of Sendmail macros it uses and generate corresponding export statements usable in the Sendmail configuration file.  By default, mc statements are generated.  If -c (--cf) is given, the statements for sendmail.cf are output.  See the next chapter for the detailed description of this mode.

You can pass any additional arguments to mailfromd by editing ARGS variable near line 22.

The script is not installed by default.  You will have to copy it to the directory where your system start-up scripts reside and ensure it is called during the system startup and shut down.  The exact instructions on how to do so depend on the operating system you use and are beyond the scope of this manual.

Using mailfromd with Various MTAs
*********************************

The following sections describe how to configure various Milter-capable MTAs to work with mailfromd.

Using mailfromd with Sendmail.
==============================

This chapter assumes you are familiar with Sendmail configuration in general and with Milter configuration directives in particular.  It concentrates only on issues, specific for mailfromd.

To prepare Sendmail to communicate with mailfromd you need first to set up the milter port. This is done with INPUT_MAIL_FILTER statement in your Sendmail file:

     INPUT_MAIL_FILTER(`mailfrom', `S=unix:/usr/local/var/mailfromd/mailfrom')

Make sure that the value of S matches the value of listen statement in your mailfromd.conf file (see listen).  Notice, however, that they may not be literally the same, because listen allows to specify socket address in various formats, whereas Sendmail's S accepts only milter format.

If you prefer to fiddle directly with sendmail.cf file, use this statement instead:

     Xmailfrom, S=unix:/usr/local/var/mailfromd/mailfrom

If you are using Sendmail version 8.14.0 or newer, you may skip to the end of this section.  These versions implement newer Milter protocol that enables mailfromd to negotiate with the MTA the macros it needs for each state.

Older versions of Sendmail do not offer this feature.  For Sendmail versions prior to 8.14.0, you need to manually configure Sendmail to export macros you need in your mailfromd.mf file.  The simplest way to do so is using rc.mailfromd script, introduced in the previous chapter. Run it with macros command line argument and copy its output to your sendmail.mc configuration file:

     $ rc.mailfromd macros

If you prefer to work with sendmail.cf directly, use -c (--cf) command line option:

     $ rc.mailfromd macros -c

Finally, if you use other mailfromd script file than that already installed (for example, you are preparing a new configuration while the old one is still being used in production environment), give its name in the command line:

     $ rc.mailfromd macros newscript.mf
     # or:
     $ rc.mailfromd macros -c newscript.mf

If you use this method, you can skip the rest of this chapter. However, if you are a daring sort of person and prefer to do everything manually, follow the instructions below.

First of all you need to build a list of macros used by handlers in your mailfromd.mf file.  You can obtain it running mailfromd --dump-macros.  This will display all macros used in your handlers, grouped by handler name, for example:

     envfrom i, f, {client_addr}
     envrcpt f, {client_addr}, {rcpt_addr}

Now, modify confMILTER_MACROS_HANDLER macros in your mc file.  Here, HANDLER means the uppercase name of the mailfromd handler you want to export macros to, i.e. the first word on each line of the above mailfromd --dump-macros output.  Notice, that in addition to these macros, you should also export the macro i for the very first handler (rc.mailfromd macros takes care of it automatically, but you preferred to do everything yourself...)  It is necessary in order for mailfromd to include Message-ID in its log messages (see Message-ID).

For example, given the above macros listing, which corresponds to our sample configuration (see Filter Script Example), the sendmail.mc snippet will contain:

     define(`confMILTER_MACROS_ENVFROM',dnl
     confMILTER_MACROS_ENVFROM `, i, f, {client_addr}')
     define(`confMILTER_MACROS_ENVRCPT',dnl
     confMILTER_MACROS_ENVRCPT `, f, {client_addr}, {rcpt_addr}')

Special attention should be paid to s macro (HELO domain name).  In Sendmail versions up to 8.13.7 (at least) it is available only to helo handler.  If you wish to make it available elsewhere you will need to use the method described in HELO Domain

Now, if you are a really daring person and prefer to do everything manually and to hack your sendmail.cf file directly, you certainly don't need any advices.  Nonetheless, here's how the two statements above could look in this case:

     O Milter.macros.envfrom=i, {auth_type}, {auth_authen}, \
        {auth_ssf}, {auth_author}, {mail_mailer}, {mail_host}, \
        {mail_addr} ,{mail_addr}, {client_addr}, f
     O Milter.macros.envrcpt={rcpt_mailer}, {rcpt_host}, \
        {rcpt_addr} ,i, f, {client_addr}

Using mailfromd with MeTA1.
===========================

MeTA1 (http://www.meta1.org) is an MTA of next generation which is designed to provide the following main features:

  * Security

  * Reliability

  * Efficiency

  * Configurability

  * Extendibility

Instead of using Sendmail-compatible Milter protocol, it implements a new protocol, called policy milter, therefore an additional program is required to communicate with mailfromd.  This program is a Pmilter--Milter multiplexer pmult, which is part of the Mailfromd distribution.  See pmult, for a detailed description of its configuration.

The configuration of Meta1--Mailfromf interaction can be subdivided into three tasks.

 1. Configure mailfromd

     This was already covered in previous chapters.  No special MeTA1-dependent configuration is needed.

 2. Configure pmult to communicate with mailfromd

     This is described in detail in pmult.

 3. Set up MeTA1 to communicate with pmult

     The MeTA1 configuration file is located in /etc/meta1/meta1.conf. Configure the smtps component, by adding the following section:

          policy_milter {
              socket {
                  type = TYPE;
                  address = ADDR;
                  [path = PATH;]
                  [port = PORT-NO;]
              };
              [timeout = INTERVAL;]
              [flags = { FLAG };]
          };

     Statements in square brackets are optional.  The meaning of each instruction is as follows:

     type = TYPE
          Set the type of the socket to communicate with pmult. Allowed values for TYPE are:

          inet
               Use INET socket.  The socket address and port number are set using the address and port statements (see below).

          unix
               Use UNIX socket.  The socket path is given by the path statement (see below).

          Notice, that depending on the type setting you have to set up either address/port or path, but not both.

     address = ADDR
          Configure the socket address for type = inet.  ADDR is the IP address on which pmult is listening (see listen statement).

     port = PORT-NO
          Port number pmult is listening on (see listen statement).

     path = SOCKET-FILE
          Full pathname of the socket file, if type = unix.

     timeout = INTERVAL
          Sets the maximum amount of time to wait for a reply from pmult.

          The behavior of smtps in case of time out depends on the flags settings:

     flags = { FLAG }

          FLAG is one of the following:

          abort
               If pmult does not respond, abort the current SMTP session with a 421 error.

          accept_but_reconnect
               If pmult does not respond, continue the current session but try to reconnect for the next session.

For example, if the pmult configuration has:

     listen inet://127.0.0.1:3333;

then the corresponding part in /etc/meta1/meta1.conf will be

     smtps {
         policy_milter {
             socket {
                 type = inet;
                 address = 127.0.0.1;
                 port = 3333;
             };
             ...
         };
         ...
     };

Similarly, if the pmult configuration has:

     listen unix:///var/spool/meta1/pmult/socket;

then the /etc/meta1/meta1.conf should have:

     smtps {
         policy_milter {
             socket {
                 type = unix;
                 path = /var/spool/meta1/pmult/socket;
             };
             ...
         };
         ...
     };

Using mailfromd with Postfix
============================

To configure postfix to work with your filter, you need to inform it about the socket your filter is listening on. The smtpd_milters (or non_smtpd_milters) statement in /etc/postfix/main.cf serves this purpose.  If the filter is to handle mail that arrives via SMTP, use smtpd_milters.  If it is to handle mail submitted locally to the queue, use non_smtpd_milters.  In both cases, the value is a whitespace-separated list of socket addresses.  Note, that Postfix syntax for socket addresses differs from that used by Sendmail and mailfromd.  The differences are summarized in the following table:

Table: Socket addresses in various formats

Sendmail   Mailfromd   Postfix
inet:PORT@HOST
inet://HOST:PORT
inet:HOST:PORT
unix:FILE
unix://FILE
unix:FILE

For example, if your mailfromd listens on inet://127.0.0.1:4111, add the following to /etc/postfix/main.cf:

     smtpd_milters = inet:127.0.0.1:4111

Mailfromd uses Milter protocol version 6.  Postfix, starting from version 2.6 uses the same version.  Older versions of Postfix use Milter protocol 2 by default.  Normally, it should not be a problem, as mailfromd tries to detect what version the server is speaking.  If, however, it fails to select the proper version, you will have to instruct Postfix what version to use.  To do so, add the following statement to /etc/postfix/main.cf:

     milter_protocol = 6

The way Postfix handles macros differs from that of Sendmail. Postfix emulates a limited subset of Sendmail macros, and not all of them are are available when you would expect them to.  In particular, the i macro is not available before the DATA stage, which brings two consequences.  First, mailfromd log messages will not include message ID until the DATA stage is reached.  Secondly, you cannot use i in handlers connect, helo, envfrom and envrcpt,

If you wish to tailor Postfix defaults to export the actual macros used by your filter, run mailfromd --dump-macros and filter its output through the postfix-macros.sed filter, which is installed to the PREFIX/share/mailfromd directory, e.g.:

     $ mailfromd --dump-macros | \
       sed -f /usr/share/mailfromd/postfix-macros.sed
     milter_helo_macros = {s}
     milter_mail_macros = {client_addr} {s} {f}
     milter_rcpt_macros = {rcpt_addr} {f} {client_addr}
     milter_end_of_data_macros = {i}

Cut and paste its output to your /etc/postfix/main.cf.

For more details regarding Postfix interaction with Milter and available Postfix configuration options, see Postfix before-queue Milter support (http://www.postfix.org/MILTER_README.html).

calloutd
********

     [file calloutd.texi not included]

mfdbtool
********

     [file mfdbtool.texi not included]

mtasim --- a testing tool
*************************

     [file mtasim.texi not included]

Pmilter multiplexer program.
****************************

     [file pmult.texi not included]

How to Report a Bug
*******************

     Documentation is like sex: when it is good, it is very, very
     good; and when it is bad, it is better than nothing.

     Dick Brandon

Although the author has tried to make this documentation as detailed as is possible and practical, he is well aware that the result is rather ``better than nothing'', than ``very good''.  So, if you find that some piece of explanation is lousy or if you find anything that should have been mentioned here, but is not, please report it to bug-mailfromd@gnu.org.ua.

Similarly, if the program itself fails to meet your expectations, or does not do what is described in this document; if you have found a bug or happen to have any suggestion... or have written a useful function you wish to share with the rest of mailfromd users, or wish to express your thanks, email it to the same address, bug-mailfromd@gnu.org.ua.

If you think you've found a bug, please be sure to include maximum information needed to reliably reproduce it, or at least to analyze it.  The information needed is:

  * Version of the package you are using.

  * Compilation options used when configuring the package.

  * Run-time configuration (mailfromd.mf file and the command line options used).

  * Conditions under which the bug appears.

Gacopyz
*******

     [file gacopyz.texi not included]

Time and Date Formats
*********************

     [file strftime.texi not included]

Upgrading
*********

     [file upgrade.texi not included]

GNU Free Documentation License
******************************

     [file fdl.texi not included]

Concept Index
*************

This is a general index of all issues discussed in this manual