I've created a closed community,
mmsbeta, for test messages and the like.
Implementation decisions have been made as follows: I will be developing the gateway in C#, and will be using a POP3 interface to the mail server. All configuration files will be XML. I may implement IMAP as well, but as the application is intended to be portable POP3 seems to be a better initial target - also it's relatively easy to scan a mailbox for known headers and extract using POP3.