XMail

XMail is a free POP3/ESMTP Internet / Intranet e -mail server for Unix, Linux and Microsoft Windows operating systems.

It is a slender, robust and faster e- mail server. Several filter interfaces make XMail to a very flexible tool. Filters can be implemented in any programming language that can process the command line arguments and return error codes. In addition, there is an interface to almost all server functions to remote maintenance.