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