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.
NethServer - NethServer is an operating system for Linux enthusiasts, designed for small offices and medium...
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
ClearOS - A very good alternative for Windows Server, for free
Roundcube - Web-based IMAP email client
FreeIPA - FreeIPA is an integrated security information management solution combining Linux (Fedora), 389...