SpamAssassin is a mail filter that can be used on a wide variety of email systems including procmail, sendmail, Postfix, qmail, and many others. It works by identifying spam using a variety of mechanisms including text analysis, Bayesian filtering, DNS blocklists, and collaborative filtering databases.

SpamAssassin is a mail filter or classifier. It will examine each message presented to it, and assign a score indicating the likelihood that the mail is spam. An external program must then examine this score and do any routing the user wants done. There are many programs that will easily perform these functions after examining he score assigned by SpamAssassin.

SpamAssassin is a project of the Apache Software Foundation.