hMailServer is an email server for Microsoft Windows. It allows you to handle all your email yourself without having to rely on an Internet service provider (ISP) to manage it. Compared to letting your ISP host your email, hMailServer adds flexibility and security and gives you the full control over spam protection.
The hMailServer project was started in late 2002 by Martin Knafve. Since then, it has become one of the most popular email servers for Windows. From the start, the focus has been to create an easy-to-use email system that includes all the basic features you need. The project started on SourceForge.net, but moved later to it's own website.
hMailServer is free, and all the source code is on GitHub.