Semi's Spam Milter (sspamm), is python based SPAM filter for Sendmail that utilizes spambayes heurestic spam filtering. You also need Python Milter and Spambayes.
I don't know if there is anyone else who is using Sspamm to filter mail. I have been using it for almost 10 years for now, and I do like it ... I would like to know if there is more users of Sspamm, and what do they think? Is there any problems? Requests? Something? ... Or please, just say hi, that I know I'm not alone. :)