SpamAssassin provides you with a way to reduce, if not completely eliminate,
Unsolicited Bulk Email (or "spam") from your incoming email. It can be
invoked by a MDA such as sendmail or postfix, or can be called from a procmail
script, .forward file, etc. It uses a genetic-algorithm-evolved scoring system
to identify messages which look spammy, then adds headers to the message so
they can be filtered by the user's mail reading software. This distribution
includes the spamd/spamc components which considerably speeds processing of
mail.