Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
SpamAssassin - Use this program to "Unspam" your mailbox(es).
mailcow - An open source mailserver suite.
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
Roundcube - Web-based IMAP email client
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...