Filtering Mail with PerlMx
by Mike DeGraw-BertschOctober 10, 2001
Introduction
PerlMx is a utility by ActiveState that allows Perl programs to interface with Sendmail connections. It's quite a powerful tool, and once installed, it's very easy to use. This article will detail how to install and setup PerlMx, and provide an overview both of what you can do with PerlMx, and how to do it. This overview will be based on spamNX, the anti-spam code I developed, available at https://sourceforge.net/projects/spamnx. My next PerlMx article will go through spamNX in depth, to demonstrate how to harness the power of PerlMx.
Prerequisites
PerlMx is made possible by the excellent Milter code provided in
Sendmail versions 8.10.0 and higher. This code, when compiled into
Sendmail, allows external programs to hook into the Sendmail
connection process via C callbacks. PerlMx passes these C hooks to
the Perl interpreter, where you can access the information with a
simple shift.
Versions 8.12 and higher of Sendmail
enable Milter by default. In prior versions, you must first enable
the code in Sendmail. To do so, go to the devtools/site
directory off of the Sendmail source code. Add the following lines to
your site.config.m4 file:
|
|
dnl Milter APPENDDEF(`conf_sendmail_ENVDEF', `-D_FFR_MILTER=1') APPENDDEF(`conf_libmilter_ENVDEF', `-D_FFR_MILTER=1')
Now compile and install Sendmail. Once installed, add the following
lines to your config.mc file (again, for Sendmail below version
8.12):
define(`_FFR_MILTER','1')dnl INPUT_MAIL_FILTER(`<filter_name>', `S=inet:3366@localhost, F=T')
Be warned that if you enable Milter in your configuration file, all Sendmail connections will fail unless PerlMx is running. So wait until your code is ready to go before you change your config file.
Your Sendmail installation is now ready to go. PerlMx also needs Perl 5.6.0 or higher, with ithreads enabled, and cannot have big integer (nor really big) support enabled. Prior to 5.6.1, PerlMx will also need the File-Temp module installed. With Perl properly configured, run the installation program provided by ActiveState.
Once PerlMx is installed and your code is ready to go, run:
pmx <package> &
To launch PerlMx. At this point, you can safely turn on the Milter code in your Sendmail configuration. There are a few command-line options available for PerlMx. Most are unnecessary, but I've found I need to allow more than the default five threads. To do so, run:
pmx -r <# of threads> <package> &
You can read about all the available options by running pmx -h.
ActiveState has an FAQ available if you run into any trouble or have questions that aren't covered here.
Sendmail, Perl, and PerlMx should now be installed and ready to go. The following section provides an overview of how to write PerlMx code.
Programming Overview
PerlMx allows you to hook into the connection at many stages of the connection, which are called by PerlMx from your code. I'll now go through an outline of spamNX, to show how to start using PerlMx.
package spamNX; use strict; use PerlMx;
The basic building blocks: give your package a name, and tell it to use PerlMx. Code executed here is only run once, so you can open a database connection or perform similar operations here.
sub new {
return bless {
NAME => "spamNX",
CONNECT => \&cb_connect,
HELO => \&cb_helo,
ENVFROM => \&cb_from,
ENVRCPT => \&cb_rcpt,
HEADER => \&cb_header,
BODY => \&cb_body,
EOM => \&cb_eom,
ABORT => \&cb_abort,
CLOSE => \&cb_close,
}, shift;
}
This sub returns a blessed instance of your package's subroutines. Each key in the hash relates to a specific point in the SMTP connection, and the associated function is called at that point in the connection. Your program may define any or all of the above functions; if it isn't defined in your blessed return, PerlMx won't try to run any code.
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