SpamAssassin is an open source project that serves as an email filter to identify Spam. SpamAssassin uses a variety of mechanisms including header and text analysis, Bayesian filtering, DNS blocklists, and collaborative filtering databases. SpamAssassin runs on a server, and filters spam before it reaches your mailbox.
If you send an email to someone that has SpamAssassin you will receive a page to confirm your identity in order for you email to get to the recipients in-box. You only need to fill out the form once unless the recipient has denied your previous request.
Download SpamAssassin
Spam Assassin FAQ
THIS SOFTWARE IS FOR SERVERS ONLY AND NOT DESKTOPS.