This is part of a feature I'm working on for my service, Port87. Single user domains would work the way labels work in the @port87.com accounts. So all you'd ne

This is part of a feature I'm working on for my service, Port87. Single user domains would work the way labels work in the @port87.com accounts. So all you'd need to do to send from an address like "myaddress@example.com" is create a label called "myaddress". I don't have the custom domains feature ready yet, but once I launch it, it sounds like it would fit your needs.