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courierperlfilter(8)

NAME

   courierperlfilter - Sample Perl-based mail filter

SYNOPSIS

   filterctl [[start] | [stop]] [perlfilter]

DESCRIPTION

   This is an example global mail filter that uses an embedded Perl
   script. "Embedded" means that the Perl interpreter is loaded once, and
   the same Perl code is repeatedly called to accept or reject incoming
   messages, one by one. Perl filtering is relatively time consuming
   (compared to filtering in C or C++), and excessive delays in mail
   filters result in incoming mail being deferred (rejected with a
   temporary error code). Therefore the perlfilter wrapper can create
   multiple perlfilter processes, so that multiple processes are used to
   filter incoming mail.

   perlfilter requires Perl 5.10 or higher. The best way to create a Perl
   filter is to start with the sample filter,
   /usr/lib/courier/perlfilter-example.pl. This filter reject messages
   that contain an excessively long Date: header (designed to crash
   certain poorly-written mail clients). Use it as a basis for writing
   your own filter. You can install your filter in any convenient
   location, then initialize the /etc/courier/filters/perlfilter
   configuration file, as described below. Run filterctl start perlfilter
   to activate filtering (if necessary, run courierfilter start to start
   the mail filtering subsystem).

   Setting up a Perl script
   Most of the ugly details of connecting the Perl script to Courier's
   mail filtering engine is taken care of by the sample
   perlfilter-example.pl script. One big no-no: the script MAY NOT change
   the current directory. Anything else goes, for the most part. Loading
   other modules and classes, pretty much anything else you can do with
   Perl, is allowed.

   The Perl script, just like any other mail filtering module, receives a
   pointer to a data file and one or more control files, each time a
   message is submitted to Courier for delivery. The sample script calls
   the filterdata() function to process the data file. The data file
   contains the actual message. The filtercontrol() function is called to
   process each control file. The control file contains recipient and
   message metadata. There may be more than one control file for each
   message. The example script includes an implementation of filterdata()
   that blocks messages with corrupted headers. The example script doesn't
   do anything interesting with filtercontrol().

   filterdata() and filtercontrol() must return an empty string if no
   serious objections are raised for this message. Any other return string
   is interpreted as an SMTP-style error code that is used to reject the
   message. Care must be taken that any error messages are formatted
   strictly according to the format of SMTP error messages (even though
   the message may not actually come in via SMTP).

CREDITS

   A lot of the Perl glue code is based on examples from the perlembed
   manual page, and other sources.

FILES

   perlfilter uses the following configuration files. Changes to the
   following files do not take effect until the filter has been stopped
   and restarted.

   /etc/courier/filters/perlfilter-mode
       If this file exists and contains the word "all", perlfilter will
       create its socket in /var/lib/courier/allfilters, otherwise the
       socket will be created in /var/lib/courier/filters, see
       courierfilter(8)[1] for more information.

   /etc/courier/filters/perlfilter-numprocs
       This file contains a number that sets how many perlfilter processes
       are created. The default is 5 processes. There's always an extra
       perlfilter process that's used to clean up crashed child processes.

   /etc/courier/filters/perlfilter
       This file MUST exist and it must contain a single line of text with
       the filename of the Perl script to load.

   /usr/lib/courier/perlfilter-example.pl
       This is a sample Perl script of the kind that
       /etc/courier/filters/perlfilter points to. Use it as an example of
       writing your own Perl filters.

   /usr/lib/courier/perlfilter-ratelimit.pl
       This is a complete Perl-based filter than implements basic
       rate-limiting features.

   Please exercise good judgment in writing Perl-based filters. They
   should be reasonably fast, and do not allocate megabytes of memory.
   They should not be very promiscuous in creating global Perl variables,
   and should clean up after themselves. The current Perl wrapper does not
   destroy the Perl symbol table after each call to the filter script.
   However, do not take that for granted. This may change in the future.

AUTHOR

   Sam Varshavchik
       Author

NOTES

    1. courierfilter(8)
       [set $man.base.url.for.relative.links]/courierfilter.html

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