[Exim] frustrating relaying problem

Dear All,

Im trying to get an NT server to relay via a linux server (the linux
server has exim installed), the domain in question that we're using
to relay via has a reverse entry, and I *believe* has the correct
permissions (as far as exim is concerned) to relay via exim on
the linux server.

However I persistently get the error:

2001-03-30 05:02:36 refused relay (host) to <mike@???> from
<bob@****.co.uk> H=****.co.uk [216.*.*.*]

I've added the domain in question to /etc/localdomains and every other
conceivable place I can think of.

Am I missing anything out or making an obvious mistake here? Any help
appreciated.

Best Regards,

Jordan Gross