dmarcian - Safeguard your email from abuse
SpamAssassin - Use this program to "Unspam" your mailbox(es).
Proofpoint - Proofpoint provides cloud-based email security, e-discovery and compliance solutions for companies to protect sensitive business data.
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
PowerDMARC - Stop hackers to send emails from your domain
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...