Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
sSMTP - sSMTP is a simple MTA to deliver mail from a computer to a mail server.
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Sendmail - Sendmail is a general purpose internetwork email routing facility that supports many kinds of...
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.
Cyrus IMAP - The Cyrus IMAP server differs from other IMAP server implementations in that it is generally...