Proxmox Mail Gateway - Protect mail server against spam, viruses and malware with Proxmox Mail Gateway security for businesses, government, education and non-profit organizations.

SpamAssassin - Use this program to "Unspam" your mailbox(es).

Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...

SPAMfighter - SPAMfighter and Microsoft have built the strongest and most effective anti spam filter for Outlook, Windows Live Mail, Outlook Express & Thunderbird

SpamTitan - Comprehensive Email Protection. 99.99% Spam Detection. Blocks phishing, viruses, malware and other email threats.

MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.