Perl-based spam filter using text analysis

 SpamAssassin is a very powerful and fully configurable spam filter
 with numerous features including automatic white-listing, RBL
 testing, Bayesian analysis, header and body text analysis. It is
 designed to be called from a user's .procmail or .forward file, but
 can also be integrated into a Mail Transport Agent (MTA).
 .
 If you use spamassassin on a moderately high-volume mail server, you
 may which to consider installing the spamc and spamd packages, which
 provide a daemonized variant of spamassassin that avoids the need to
 start a full perl runtime for each message processed.