Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.

OBM - OBM is a free messaging and collaboration platform useful for just a couple to many thousands of users with strong support for mobile devices.

iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).

Microsoft Exchange Server - Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft.

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...