[commodorejohn]

Dividing up the backend and frontend Transmission-style is a good idea from a modularity/maintainability standpoint, but I can't think of a scenario where you'd need to store mail/run the daemon on one machine and access it from another that wouldn't already be covered by modern mail providers' nearly ubiquitous Web clients, so developing a bespoke Web client seems like unnecessary duplication of effort. It would make the frontend an easier lift if you only wanted browser-based mail access, but if you're planning on doing a Motif version anyway, may as well just focus on that.