Mercury Mail Transport System - The Mercury Mail Transport System is a mail server that sends and receives messages on behalf of a...
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
mailcow - An open source mailserver suite.
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.
Roundcube - Web-based IMAP email client
Sendmail - Sendmail is a general purpose internetwork email routing facility that supports many kinds of...