Ahh, sorry, I think I know what's wrong, basically the file domuser.dat is missing the alias (check by looking in it)  if that's the case (or domuser.dat is missing entirely)

 

fix thusly:

    tellmail rescan_aliases_files  

    copy domuser.newdat domuser.dat

    tellmail reload

 

That should do the trick.  If you have an existing domuser.dat save a copy of it first.

 

If that doesn't resolve things let me know.

 

    Chrisp.