[Exim] Looking up users in db file

Hi,

I was wondering if there is a way to force exim to look in a dbm or text
file for users that should be local in stead of letting him look it up in
the password file on the machine?

Hope somebody knows that cos i keep getting the following error:


This message was created automatically by mail delivery software (Exim).

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

user1@???
unknown local-part "user1" in domain "fakedom1.org"

Thx

Thierry Martens