Last Updated on: 19th November 2023, 01:34 pm

Web site:
Category: Network
Subcategory: Address Books, Calendars, E-mail, Forums, Instant Messengers, RSS, Wiki
Platform: BSD, Linux, UNIX-like
License: GPL
Interface: Web UI, CLI
First release: < 1988

Citadel – an open source collaboration messaging and groupware suit which is designed to run on open source operating systems such as Linux or BSD. Citadel is a highly integrated Groupware Platform with a AJAX-powered “Web 2.0” interface, but also providing SMTP, IMAP, POP3 and GroupDAV access to its content.

Citadel offers versatile email services with very low administration needed. It provides its own implementations of these server protocols: IMAP, POP3, SMTP, ManageSieve, XMPP, Citadel.

Citadel provides features such as:
– Email, calendaring, address books, bulletin boards, instant messaging, and more … all in one tightly integrated server package. Unlike other open source groupware systems, all of Citadel’s data stores are built-in. All that tedious mucking about with dependencies and config files is a thing of the past.
– High-performance, multiprotocol, multithreaded server engine
– Wiki and blog engines built in. Citadel is a collaboration server and a content management system!
– Web browser, telnet/SSH, local client software accessible
– Standards-compliant e-mail built in: IMAP, POP3, ESMTP
– Group calendaring and scheduling (WebDAV, GroupDAV, and Kolab-1 compatible)
– Built-in listserv (mailing list server)
– Built-in RSS Feed Aggregation
– Integrated server-side mail sorting and filtering. Users can choose between an easy-to-use web based rules editor, or the power of writing complex scripts using the industry standard Sieve language.
– Support for push e-mail and mobile devices
– Database-driven, single-instance message store
– Built-in full text index for fast searching
– Authenticated SMTP for remote email submission
– Multiple domain support
– Built-in integration with perimiter email filtering technologies such as Realtime Blackhole Lists (RBL’s), SpamAssassin, and ClamAV antivirus
– Server-to-server replication. Users in any number of domains can be spread out across any number of Citadel servers, allowing you to put data where you need it, and enabling infinite horizontal scalability.
– Web-based access to email, calendars, and everything else through a powerful AJAX-style front end
– Very strong support for “public folders” and message forums.
– Built-in instant messenger service
– SSL/TLS encryption for all protocols

The Citadel system is extremely versatile. It provides numerous front ends to present to users, such as a text-based interface, an AJAX-style web interface, and many popular PIM clients using SMTP/POP/IMAP.

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