Citadel

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.

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

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).