AMaViS (A Mail Virus Scanner) scans e-mail attachments for viruses using third-party virus scanners available for UNIX environments. It resides on a UNIX (Linux) machine and looks through the attached files arriving via e-mail, generates reports when a virus is found and sets the delivery on hold.
AUC (Authenticated User Community) is an intranet system designed for use in an educational organization but is also useful in many other settings. It offers the ability for users to have a uniform web-based interface to discussion forums, e-mail (similar to hotmail, etc.), file management, and a searchable user database. Also, "Interactive Classrooms" provide a means for students and teachers to have a web-based extension to their in-class interaction. The system runs from a C-based monolithic CGI script. MySQL is used for database storage. Also, the web-based mail client supports MIME parts/attachments, IMAP, mbox, and multiple mail folders.
Citadel is an advanced messaging and collaboration system for groupware and BBS applications. Users can connect to Citadel using any telnet, WWW, or client software. Among the features supported are public and private message bases (rooms), electronic mail, real-time chat, paging, shared calendaring, address books, mailing lists, and more. Unlike other collaboration servers, Citadel provides its own data stores and is therefore extremely easy to install; you don't have to "bring your own" email and database because they're built in. The server is multithreaded and scalable. In addition, SMTP, IMAP, and POP3 servers are built-in for easy connection to Internet mail. Citadel is both robust and mature; it has been in production since 1987.
The Courier mail transfer agent (MTA) is an integrated mail/groupware server based on open commodity protocols such as ESMTP, IMAP, POP3, LDAP, SSL, and HTTP. Courier provides ESMTP, IMAP, POP3, Webmail, and mailing list services within a single consistent framework. Individual components can be enabled or disabled at will. Courier implements basic Web-based calendaring and scheduling services integrated in the Webmail module.
Courier-IMAP is a lightweight server that provides IMAP access to maildir mailboxes. It supports folders, custom authentication modules, and virtual mailboxes. A compatible POP3 server is also provided. The source code is based on the IMAP module in the Courier Mail Server, but this build is independently repackaged to work with any other MTA that delivers to maildir format mailboxes.