Rumble Mail Server for Linux, Windows, you name it.

Rumble is a mail server suite for SMTP (ESMTPSA), HTTP, POP3 and IMAP4v1 with an extensive C/C++ and Lua API for scripting.
It comes with support for SSL/TLS, SQLite and MySQL and has a web-based administration and webmail feature.
Additional included modules feature greylisting, DNS blacklisting, SpamAssassin support and dynamic performance scaling as well as a multithreaded structure that allows for clustering of multiple servers for one or all domains, and with the ease of the Lua API, you can create your own new server mailing lists, CRM software, e-marketing and other extensions within minutes.

  

It's written in ANSI C with a modular approach to most services and mail extensions.

Among other wonderful things, Rumble supports the following services:

• SMTP Server or Relay:
  • Real-time whitelisting, greylisting and blacklisting (through modules)
  • Bounce Address Tag Validation and Variable Envelope Return Path (BATV + VERP)
  • Support for ESMTP extensions: AUTH, DSN, DELIVERBY, SIZE, PIPELINING, 8BITMIME
  • GLOB'ed usernames and domains ( fx. *@domain.tld or t?st@*.domain.tld)
  • IPv4 and IPv6 support
• POP3/IMAP4v1 Server:
  • The usual stuff; MD5/PLAIN logins, STARTTLS etc etc
  • Partial support for the LEMONADE profile for mobile devices.
• Modular extensions:
  • C/C++ API for developing custom-made features
  • Lua scripting environment for creating Lua-powered modules and services.
  • Bundled extensions include:
    • Dynamic performance scaling
    • Blacklisting
    • Greylisting and whitelisting
    • SpamAssassin email analyser
• Run-as-service:
  • You can run Rumble as a Windows service, a UNIX daemon, or as a regular stand-alone program in your shell or command prompt.
    On Windows, the installer app takes care of it for you - on UNIX, just use rumble --service to run it as a daemon.
• Intuitive web-interface:
  • Rumble is bundled with RumbleLua, a Lua scriptlet module that adds a web-interface to your mail server.

You can add whatever services you'd like through the module API, which allows you to write or use modules that can attach themselves to each specific aspect of mail handling, such as mailing lists, MX backup, spam and virus filtering, automatic replies and so forth.

Go visit https://sourceforge.net/projects/rumbleserver/ for moar stuff :>