SpamAssassin is a mail filter to identify spam. See http://SpamAssassin.org/ for more details.
This flexible and powerful set of Perl programs, unlike older spam filtering approaches, uses the combined score from multiple types of checks to determine if a given message is spam.
Its primary features are:
- Header tests
- Body phrase tests. For more information, see SpamAssassinRules.
- Bayesian filtering (BayesFaq)
- Automatic address whitelist/blacklist (AutoWhitelist)
- Manual address whitelist/blacklist (ManualWhitelist)
- Collaborative spam identification databases (DCC, Pyzor, Razor2); See NetworkTests.
- RBL (Realtime Blackhole Lists)
- DNS Blocklists. See DnsBlocklists
- Character sets and locales
Even though any one of these tests might, by themselves, mis-identify a ham or spam, their combined score is terribly difficult to fool.