Anti-Spam SMTP Proxy Server implements multiple spam filters
Provides mechanisms for walking through any arbitrary PHP variable
PHP Email address validator
Anti Spam SMTP Gateway
Fast Bayesian spam filter along lines suggested by Paul Graham
SMTP email proxy and relay server
Remote anti spam utility
RBL script for server checking
An easy-to-use anti-spam email gateway
Open source DMARC implementation
Secure mail + Tor gateway
Virtual Appliance of RadicalSpam
Open Source Anti-Spam and Anti-Virus Gateway
OpenSource high performance mail policy daemon for Postfi
javascript to convert thunderbird/seamonkey filters to sieve rules
CRM114 milter for sendmail
QSF milter for sendmail
AV/content filter for Qmail