The Anti-Spam SMTP Proxy (ASSP) aims to be an open-source SMTP Proxy server with auto-whitelists, self-learning Bayesian, greylisting, virus scanning, attachment blocking, and many other filter methods.

Some of its other many, geeky features include multiple weighted DNSBLs and URIBLs, greylisting, regular expression filtering, penalty box, senderBase, attachment blocking, ClamAV and FileScan included, blocking reporting, LDAP support, backscatter detection and more.