[2]Zentyal (previously known as eBox Platform[3]) is a open source email and groupware solution based on Ubuntu Linux.

[7] Zentyal implements the Microsoft Exchange Server protocols on top of standard open source components (such as Dovecot, Postfix, Samba, etc.)

As of release 5, Zentyal has dropped native compatibility with Microsoft Outlook using the MAPI protocol via OpenChange, due to unspecified issues.

The email and groupware protocols supported by Zentyal are ActiveSync, SMTP, POP, IMAP, CalDAV, CardDAV and Active Directory.

Zentyal Server has a development edition that is freely downloadable and its source code is available under terms of the GNU General Public License.