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

Mutt - Mutt is a small but very powerful text-based mail client for Unix operating systems.

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.

Alpine - Alpine is a fast, easy to use email client that is suitable for both the inexperienced email user...

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.

Mailspring - Mailspring is a mail client for Mac, Windows and Linux.