SpamAssassin - Use this program to "Unspam" your mailbox(es).
Mimecast Gateway - Mimecast Gateway is a SaaS-based email security solution that uses sophisticated, multi-layered detection engines and intelligence to protect email data and employees from malware, spam, advanced threats and zero-day attacks.
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...
dmarcian - Safeguard your email from abuse
Oikik Antispam - Oikik is a cloud-based email filtering service that works with your existing email service.
Hornetsecurity - Hornetsecurity offers you comprehensive, integrated managed e-mail security services.