1. Double check the error handling and review error message in various
   failure modes.
2. Implement the CHUNKING extension (rfc 3030; as soon as I find an
   SMTP server that supports it).
3. Better error message (translated standard meanings of the known
   response codes, ENHANCEDSTATUSCODES extension (rfc2034)).
4. (KIO) MultiPutJob to support pipelining across messages.
5. Ged rid of slave's header generation after checking who on earth
   uses that...

and further refactoring to make the code pleasant to look at ;-)
