Mailafar is a mail server designed for use in difficult communication environments providing a full set of Internet email protocols, web mail, web admin, dial-in and wireless LAN access control. It will run on Linux, FreeBSD and Windows.
This is an email server written in C#. The server handles protocol, and a plugin architecture allows developers to create their own authentication/mail storage system, making this one of the most scalable email servers in the world. 2 plugins included.