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.
Rumble Mail Server Web Site
Wiki: Feeding emails to external programs
Wiki: Lua API
Wiki: Setting up Rumble
Wiki: Writing your own modules for Rumble