Hi,
SmarterMail is a commercial piece of software covered by SmarterTools' End User License Agreement (EULA), and not open source. While it is fully API-driven, which allows users to integrate it with virtually any other product, customizing SmarterMail or making custom changes is simply not allowed by our EULA.
That said, what is it you're trying to accomplish? "Custom changes to the mail service" is a bit broad.
Derek Curtis
COO
SmarterTools Inc.
www.smartertools.com