This is the software publisher's description.

MDaemon email server for Windows is the best choice for managing your organization's messaging and collaboration infrastructure.

The MDaemon email server for Windows is a comprehensive messaging and collaboration solution that provides secure, standards-compliant features to small-to-medium sized businesses. It supports mailing lists, remote access and administration, spam-blocking, content filtering, and multiple domain support.

As a reliable and scaleable groupware solution, the MDaemon email server for Windows delivers solid performance from its feature-rich and user-friendly design, and supports IMAP, SMTP, and POP3 protocols. Solid security capabilities are at the core of MDaemon with anti-spam functionality, content filtering, blacklists and whitelists, and reverse DNS lookups. The MDaemon email server for Windows maintenance and administration features are easy and user-friendly with list server support, intuitive user interfaces, LDAP functionality for contact management, attachment blocking by file type, email address aliases, and server-based client email handling rules.

Note that this is the free version of MDaemon that enables you to setup a 5-user mail sorting and filtering system for your small office or department. The Free version requires a serial code which you can obtain from this page.