SpamHero - SpamHero is a professional spam filtering accuracy while lowering the cost to domain and business owners.
SpamAssassin - Use this program to "Unspam" your mailbox(es).
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.
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...
Mimecast - Utilities, Application Utilities, and Security