SpamBayes is a tool used to segregate unwanted mail (spam) from the mail you
want (ham). Before SpamBayes can be your spam filter of choice you need to
train it on representative samples of email you receive. After it's been
trained, you use SpamBayes to classify new mail according to its spamminess
and hamminess qualities.

WWW: http://spambayes.sourceforge.net/