hMailServer was a free email server for Windows created by Martin Knafve. It ran as a Windows service and includes administration tools for management and backup. It had support for IMAP, POP3, and SMTP email protocols. It could use external database engines such as MySQL, MS SQL or PostgreSQL, or an internal MS SQL Compact Edition engine to store configuration and index data. The actual email messages were stored on disk in a raw MIME format. As of January 15th, 2022, active support and development were officially halted, although version 5.6 will continue to receive updates for critical bugs.
Common features such as multiple-domain support, aliases, catch-all and basic mailing lists were present. Users could be authenticated both against the local hMailServer user system and against an external Active Directory.
AntiSpam
hMailServer offered a number of different AntiSpam mechanisms:
Host based DNS Blacklisting (DNSBL) URL based DNS blacklisting (SURBL) Greylisting (must retry sending for the message to succeed) SPF Built in SpamAssassin integration DKIM (in version 5.1)
AntiVirus
hMailServer had built in support for ClamWin/ClamAV. It's possible to execute any command line virus scanner.
Other features
Domain and account signatures (for legal and advertising footers) Server side rules (rules for individual accounts available in v5) Retrieval of messages from external POP3 accounts Quotas on domain, mailbox, and individual message sizes Plus addressing (using + to make a virtual alias for an account specific to a task, as seen in Gmail) Attachment blocking (based on attachment extension) Custom SMTP routes for specific domains (can be used to set up MX backup, forwarding and more) API (it's possible to write hMailServer scripts using VBScript and JScript) Built-in support for SSL
Integration
ClamAV anti-virus software
SquirrelMail for webmail, (requires IIS or Apache); spell-checking available
Roundcube for webmail, also requires auxiliary database provider such as mySQL to operate SpamAssassin spam filtering
History
The hMailServer project was started in 2003. Up until 2008 and version 4, the project was licensed under the GPL. Versions 5.0 to 5.3 were proprietary. Since version 5.4, hMailServer is licensed under the GNU AGPL 3.
The latest version of hMailServer appears to be open source again. This is also noted on the hMailServer home page.