- correct handling of sender-visibility flag when receiving message (and also use correct address for billing. no spoofing).
- In content adaptation: Colour depth adjustment
- Need to parameterise some values: tmp dir, response messages (say on failed content adaptation)
- Test suite
- Correct handling of unrecognised mms headers. spec says pass them un-changed.

- Queue module needs to be de-coupled slightly from storage, so that mmsproxy can run on a separate box
  but be able to initiate queue writes/reads over network. Hence pieces can run on separate boxes 
  (with mmsrelay providing network service for queue functions)