Kolab is a free and open source groupware suite. It consists of the Kolab server and a wide variety of Kolab clients, including KDE PIM-Suite Kontact, Roundcube web frontend, Mozilla Thunderbird and Mozilla Lightning with SyncKolab extension and Microsoft Outlook with proprietary Kolab-Connector PlugIns. Basic Concepts Kolab uses IMAP as an underlying protocol for email, contact, and calendar entries. These entries are saved in IMAP folders in Kolab XML format, and the IMAP server controls storage and access rights. Configuration and maintenance of Kolab is done by LDAP. Kolab Clients and the Kolab server use well established protocols and formats for their work (i.e. IMAP as mentioned above, vCard, iCal, XML and LDAP). This allows the Kolab Format specification framework, or even portions of it, to be utilized as an open set of specifications for groupware clients and servers to communicate with each other. Third party implementations began almost immediately; for example, the Citadel groupware server began supporting version 1 of the Kolab Format specification in March 2004. The concepts on which Kolab relies are laid out in the Kolab Format Specification and Architecture Paper for Kolab 2, and for Kolab 1 in the Kroupware Contract, Architecture Paper and Technical Description. Main features Full seamless support of mixed clients environments (Outlook, KDE, Web etc.) Full server side support for ActiveSync and CalDAV, CardDAV and WebDAV Support for Email, Calendar, Address Books, Tasks and File-Cloud Support for KDE with Kontact Support for Microsoft Outlook with proprietary connector PlugIns A web administration interface Configuration data is kept in a LDAP directory A global LDAP addressbook for contacts IMAP4rev1 as well as POP3 access to mail Full support for client-side PGP and S/MIME email encryption (officially Sphinx-interoperable) Full support for shared calendars with IMAP ACLs Full support for shared contacts with IMAP ACLs Fully offline capable using KDE Kontact or Microsoft Outlook Support for server side resource management (e.g. rooms, cars) Full support for freebusy handling Kolab 3.x clients Roundcube is the default web client delivered with Kolab 3.0; KDE Kontact, starting with version 4.10 , and Kontact-Touch (K Desktop Environment, Free Software); SyncKolab , starting with version 3.0.0, is a Mozilla Thunderbird/SeaMonkey and Lightning extension (Free Software); Kolab Desktop Client is a stabilized and professionally supported version of KDE Kontact. Kolab 2.x clients KDE Kontact and Kontact-Touch (K Desktop Environment, Free Software) Horde (integrated in Kolab since v2.2.1), a web-frontend for utilising