Zentyal
Zentyal is an open source email and groupware solution based on Ubuntu Linux. The latest release took place on February 26, 2024.
Zentyal implements the Microsoft Exchange Server protocols on top of standard open source components in order to provide native compatibility with Microsoft Outlook clients. As of release 5, Zentyal has dropped native compatibility with Microsoft Outlook using the MAPI protocol via OpenChange, due to unspecified issues. The OpenChange project was discontinued in December 2015.
The email and groupware protocols supported by Zentyal are ActiveSync, SMTP, POP, IMAP, CalDAV, CardDAV and Active Directory.
Zentyal is distributed in two packages: Zentyal Server for SMBs and Zentyal Cloud for hosting providers. Zentyal Server has a development edition that is freely downloadable and its source code is available under terms of the GNU General Public License.