SOGo
SOGo is groupware server with a focus on scalability and open standards.
Zarafa
Open Source Collaboration, providing integration with your existing Linux mailserver, native mobile…
Mail-in-a-box
Mail-in-a-Box provides webmail and an IMAP/SMTP server for use with mobile devices and desktop mail software and also includes contacts and calendar synchronization.
Apple Mail
There’s big news attached.
iRedMail
A fully fledged, free email server solution, an open source project (GPL v2).
Roundcube
Web-based IMAP email client.
