ZSFA -- Son Of Sam Email Server
http://www.zedshaw.com/projects/sos/

At its core SoS is just a Python based SMTP server that can receive emails, process them using handlers based on routing regex, and then relay results out again using templates. All of this is done without using alias files, m4 macros, pipes, weird protocols, or duplicate processing of the emails. SoS just works like a flexible scripting language SMTP should operate.

Zed's nice and simple little Python-based SMTP server that dispatches to handlers much like a modern web framework, and uses Mako templates. Can relay to postfix and the like for big volume.

programmable python mail server

A Python based SMTP server that can receive emails, process them using handlers based on routing regex, and then relay results out again using templates.

This looks very exciting! I love email based services b/c it is such a great interface for users, so this seems like it could prove to reinvigorate email as a platform, which seems like the future.