I've installed some updated spam filtering on dorksville. It rocks. The guts of it is MimeDefang. Defang is a sendmail milter plugin, which lets it filter email during the SMTP transaction with the remote server. Defang calls in ClamAV antivirus and SpamAssassin to do the spam filtering.
Now this is similar to what I had set up before, except now I've turned on the RBL checks - they query some servers to find out if the host sending the email is a known spammer, and also checks every URL mentioned in the email to see if it is a known spammer website. very cool. I've also turned on Razor and Pyzor, which make a hash of the email body and check it against known spam on a central server.
Don't you just love free software?