[Exim] user authentication/rewriting

Dear all,

I am running exim 3.34 which is checking local users against a winbind
(samba/win nt) database. This all works perfectly although email addresses
have to be of the following format to be accepted.

homelet+paul@???

where homelet is the name of Windows domain, and the + sign is just a
separator.

I am trying to get exim to accept mail to : paul@??? and store it
locally owned by the user : homelet+paul. I've partially managed to acheive
this using a smartuser director as below :

# Local domain user
LocalDomainUser:
driver = smartuser
transport = local_delivery
user = homelet+$local_part

This correctly accepts all mail, if the user exists, it is stored with the
correct uid and gid, unfortunately if the user is not know on the system,
exim freezes the mail rather than just rejecting it.

Has anyone got any ideas?

Thanks in advance,

Paul