hMailServer is a free, open source mail server for Windows. It has support for SMTP, POP3, IMAP, virtual domains, anti virus scanning, distribution lists and much more. It comes with a great COM library that easily can be used for integration. Data is stored in a database server, MySQL or MS SQL, depending on your choice.
Features:
- POP3, SMTP, IMAP
- Virtual domains
- Built-in backup
- Scripting
- External accounts
- Rules
- Multilingual
- AntiVirus
- Spam protection
- Routing
- MX backup
- Mirroring
- Multihoming
- SQL-support
What's New in version 5.0 Build 321 Beta:
- It wasn't possible to display messages having an attachment with file names containing specific character.