I have what I think is an unusual outbound email issue. Most of our email sends just fine. We have a few addresses that are getting the following error in the Last Error column on the Exchange 2010 Queue Viewer:
451 4.4.0 Primary target IP address responded with 421 4.2.1 "Unable to connect". Attempted failover to alternative host, but that did not succeed. Either there are no alternative hosts or delivery failed to all alternative hosts.
Delivery Type: DnsConnectorDelivey
Most addresses deliver just fine but we are getting a few domain names that do not deliver at all (get hung up in the queue).
Running the Exchange Troubleshooting Assistant I get the following "Possible Root Cause Found":
'MSExchangeMailSubmission' service on server EAGLESBSSERVER is not discovering all servers with Hub Transport server role installed in the local Active Directory site with GUID 'fffdc295-cfe9-4c9d-83b4-0bdf0a48cf91'. This can be an indication that 'MSExchangeADTopology' discovery is failing to discover these servers due to object validation errors.
We only have one server (SBS2011)
How can I resolve this?