SpamAssassin - Use this program to "Unspam" your mailbox(es).
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
SPAMfighter - SPAMfighter and Microsoft have built the strongest and most effective anti spam filter for Outlook, Windows Live Mail, Outlook Express & Thunderbird
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...
SpamTitan - Comprehensive Email Protection. 99.99% Spam Detection. Blocks phishing, viruses, malware and other email threats.
Scrollout F1 - Scrollout is a free and easy to use anti-spam email gateway designed for Linux & Windows administrators without advanced email security experience.