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Citadel is a collaboration suite (messaging and groupware). It provides support for Email, Calendaring/Scheduling, Address books, Bulletin boards, Mailing List Server, Instant Messaging, Wiki, Multiple domain support.

Its features include:

  • 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
  • Web browser, telnet/SSH, local client software accessible
  • Standards-compliant e-mail built in: IMAP, POP3, ESMTP
  • Group calendaring and scheduling (GroupDAV and Kolab-1 compatible)
  • Built-in listserv (mailing list server)
  • 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.
  • 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
  • Citadel is true open source software. Unlike other groupware servers, it isn't a cut-down version of an expensive proprietary “pro” version. We make our very best work available to everyone on the same terms. 100% of our code is covered by the GNU General Public License (GPL3).



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