Proxmox Mail Gateway - Protect mail server against spam, viruses and malware with Proxmox Mail Gateway security for businesses, government, education and non-profit organizations.
Spamihilator - The free Anti-Spam-Filter Spamihilator removes more than 98% of spam mails before they even get into your inbox.
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...
Mailwasher - Over 8 million people use MailWasher as their spam filter
SpamAssassin - Use this program to "Unspam" your mailbox(es).
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.