hMailServer is a free email server for Windows created by Martin Knafve. It runs as a Windows service and includes administration tools for management and backup. It has support for IMAP, POP3, and SMTP email protocols. It can use external database engines such as MySQL, MS SQL or PostgreSQL, or an internal MS SQL engine to store configuration and index data. The actual email messages are stored on disk in a raw MIME format. It has active support and development forums.
Common features such as multiple-domain support, aliases, catch-all and basic mailing lists are present. Users can be authenticated both against the local hMailServer user system and against an external Active Directory.