- correct handling of sender-visibility flag when receiving message (and also use correct address for billing. no spoofing).
- Sending DLR correctly when sending from/to email.
- In content adaptation: Colour depth adjustment
- logging a la access.log  (one log per interface -- mm1-log, mm4-log, etc)
- Need to parameterise some values: tmp dir, response messages (say on failed content adaptation)