SecurityFocus has a series of tutorials on filtering email with Postfix and Procmail. This is a great tutorial and these are enormously useful programs. Postfix and Procmail to not only block SPAM but also filter and sort all kinds of messages. Checkit via the link, great stuff. Filtering E-Mail with Postfix and Procmail, Part One
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Re: Filtering email with Postfix and Procmail: securityFocus
Actually, Postfix doesn't *work with* Sendmail. Postfix is a drop-in replacement for Sendmail.
While Procmail works well, it can be a bitch and a half to set up properly. I personally use Mail::Filter; a Perl module for filtering email by Simon Cozens. It works quite well. Another alternative is TMDA, a Python-based mail filter, which uses a *whitelist* to denote who to accept mail from as opposed to a *blacklist*.
Re: Filtering email with Postfix and Procmail: securityFocus
Duly noted, Postfix is an SMTP server, my slip, thanks for correcting me, I will fix the story.