"This document describes how to install SpamAssassin (for
filtering SPAM) and ClamAV (for filtering viruses, trojans, worms,
etc.) and how to invoke them by using procmail recipes. It is
suitable for scenarios where Sendmail or Postfix deliver emails to
local users. It should work (maybe with slight changes concerning
paths etc.) on all *nix operating systems. I tested it on Debian
Woody so far.
"In the end you will have a system where Sendmail or Postfix
deliver emails to a local user; the emails are passed to procmail
which invokes SpamAssassin and ClamAV in order to filter the emails
before they arrive in the user's inbox. However, the installation
of Sendmail and Postfix are not covered in this document..."