[Exim] permanant fatal errors

One of my mail servers (NT) give the following error when some people
try to send mail.




The original message was received at Tue, 13 Mar 2001 12:47:16 -0200
(GMT)
from noka.ub.bw [168.167.X.X]

----- The following addresses had permanent fatal errors -----
<TGWERE@???>

Some users can send outside and all can receive mail from outside. I
don't know if this is a DNS problem, Exim or NT (running exchange). The
box is running solaris7