[Exim] Interesting Scene

Hi guys,
am New to this list and I have not used Exim before.
However I have something interesting,
I have a qmail MTA server which has virtual email domains say abc.co.ug,
and this Virtual Domain has the same A record as the main server.
All the MX records are fine.


Now interestingly enough anyone who has an Exim MTA server can not send
emails to this Virtual Domain abc.co.ug and yet they can send to the main
server.
Now this virtual domain can get emails from other MTA server , i have tried
it out from yahoo.com , usa.net , hotmail.com and all these can send emails
to users@???..


Then all users on my the domain abc.c.ug can send emails to the EXIM MTA
server, but once a user at the exim server hits reply he gets this as the
error message after sometime... see below

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:

user@???
Operation timed out:
retry timeout exceeded



Thanx for your help

Eric