Question : Exchange 2003 Routing issue

We have an in house exchange server 2003  for staff. We also have an external mail service  handled by a third party. We use the external mail server to handle our clients. We have our clients as cnotacts in our internal exhange server. We have a domain called DomainA. In DomainA we have a delegated subdomain that is directed to an external DNS server. This works fine both internally and externally for getting mail. Now we also have DomainB, which that is working fine internally and externally. It too has a delegated subdomain setup just the first one. The problem is that our internal exchange server will not deliver to this subdomain of DomainB. Externally you can send mail to it. Internally nslookup resolves the domain fine, tracert finds the subdoain correctly, smtpdiag finds that dns and smtp are fine to this domain, yet our exchange tells us that this email address does not exist in this domain, which it does. Externally sent from say Gmail delivers it just fine. Smtp logs log no instance of this attemtped delivery. The message tracking logs only mention an NDR was sent with id 1025 but that is it. My guess is that exchange not dns has a problem with this particular subdomain and even though dns can point it to where it needs to go, exchange is trying to find this address in one of our internal domains, even though the ns records point to our external dns, and of course will fail with no match. The external mail server this is supposed to send to has been replaced with a temp exchange sever I set up externally with the exact same results. If I add one letter to the subdomain and reset both internal and external dns servers it works fine. Is there some cache in exchange or possibly a corrupted exchange or active directory record that needs to be manually checked or set?

Answer : Exchange 2003 Routing issue

If the domain is in recipient policy then Exchange will be treating it as internal and attempting to deliver it to the addresses it finds. If you have contacts setup then unless those contacts also have external addresses on them then the email will not be delivered.

Simon.