Courier MTA

Courier MTA is a fast, scalable, open source enterprise mail and groupware server. It handles ESMTP mail transfer and provides IMAP and POP3 access, along with webmail for users who prefer to work through a web interface. The server also supports mailing lists and includes web-based calendaring and scheduling services, bringing email and several related groupware functions together in one program. It is intended for enterprises and other organizations that need to provide mail and groupware services to their users. It is particularly relevant where an organization wants to support multiple ways of accessing email, including IMAP, POP3, and webmail, while also running mailing lists from the same server. No specific paid product is identified as a direct replacement. Its main stated limitation is that the web-based calendaring and scheduling functionality is basic, rather than a more extensive part of the groupware system.