bogofilter -- Fast Bayesian Spam Filter

Bogofilter is a mail filter that classifies mail as spam or ham (non-spam) by a statistical analysis of the message's header and content (body). The program is able to learn from the user's classifications and corrections. Bogofilter provides processing for plain text and HTML. It supports multi-part MIME messages with decoding of base64, quoted-printable, and uuencoded text and ignores attachments, such as images.