ASSP - Anti-Spam SMTP Proxy

ASSP is a SMTP proxy which sits between SMTP server and the MTA. It filers the spam and delivers the legtimate mails to the MTA. Its feature include Bayesian analysis, Sender Policy Framework) validation and blocking, Realtime Blackhole Listing, URL Black Listing, Multi-level attachment blocking, LDAP support, Backscatter Detection, SNMP support and lot more.

Sourceforge: http://sourceforge.net/projects/assp/