Zimbra

The software consists of both client and server components, and at one time also offered a desktop email client, called Zimbra Desktop. Two versions of Zimbra are available: an open-source version, and a commercially supported version ("Network Edition") with closed-source components such as a proprietary Messaging Application Programming Interface connector to Outlook for calendar and contact synchronisation.

The now discontinued Zimbra Desktop was a full-featured free desktop email client. Development was discontinued under VMware's stewardship in 2013 but was restarted in February 2014, but was ended again by 2019. The web client featured an HTML5 offline mode starting with version 8.5.

The Zimbra Web Client is a full-featured collaboration suite that supports email and group calendars. At one time it featured document-sharing using an Ajax web interface that enabled tool tips, drag-and-drop items, and right-click menus in the UI. Today it has document sharing, chat, and videoconferencing. Also included are advanced searching capabilities and date relations, online document authoring, "Zimlet" mashups, and a full administration UI. It is written using the Zimbra Ajax Toolkit.

The Zimbra Server uses several open source projects (see the section, Included open source projects). It exposes a SOAP application programming interface to all its functionality and is also an IMAP and POP3 server. The server runs on many Linux distributions. It also can be run on a Windows Server, using a virtual machine and using container technology. It supports CalDAV, CardDAV and SMTP for messaging, LDAP for directory services, and Microsoft Active Directory (AD). Zimbra uses Postfix for its MTA functionality. It includes technology from ClamAV, SpamAssassin and DSPAM for anti-malware features and S/MIME for email signing and encryption. OS X Server support was dropped with version ZCS 7.0.

Zimbra can synchronize mail, contacts, and calendar items with open-source mail clients such as Mozilla Thunderbird and Evolution and also with proprietary clients such as Microsoft Outlook and Apple Mail, either through proprietary connectors or using the ActiveSync protocol, both available exclusively in the commercially supported version. Zimbra also provides native two-way sync to many mobile devices.