hMailServer

hMailServer is a free, open-source mail server for Windows operating systems created by Martin Knafve. It works as a Windows service and comes with the hMailServer Administrator tool, as well as tools for mail backup and administration. POP3, SMTP and IMAP protocols are supported. The program stores indexes and settings in a database, while the mail itself is stored on hard drives in MIME format. By default it uses its built-in Microsoft SQL Server Compact database, but it can also work with MySQL or MariaDB (for example, a server set up with the MySQL installer), Microsoft SQL Server or PostgreSQL.

The mail server supports all major functions, including virtual domains, distribution lists, aliases, server-side rules, routing, MX backup and SSL/TLS encryption. Users can authenticate through both the local user database and the Active Directory database. The program has built-in support for working with several IP addresses simultaneously, anti-spam checks such as SPF and DNS blacklists, SpamAssassin integration, ClamWin/ClamAV antivirus, or any other antivirus scanner with a command line. It is licensed under AGPLv3.

hMailServer offers a comprehensive, free mail server solution with robust features for Windows operating systems.