[Exim] Relay Problem

Hello,

I have a problem and not really sure what it is and why its happening.

I host a domain name say for example blah.com.au for a customer which has
their own mail server the main MX points to them the second to us. We are
getting the following error in the reject log file. There mail server is
up and running without any problems from what I can see ( they run
sendmail ) but a lot of people that send e-mail to this blah.com.au site
get their mail bounced back.

The error is..

2001-02-28 19:00:19 refused relay (host_accept_relay) to
<dquinn@???>
from <slgm@???> H=(mail.nbptt.zj.cn) [202.96.105.226]
------------------------------------------------------------------------------

Now I have their IP address in host_accept_relay
They have been customers for a while now and this problems is getting more
often.

Im not sure what is happening and why. Any comments/suggestions welcome
:)

Thanks in advanced..

Regards
Scott Stavretis