We are getting the error message in our queue for what looks like two domains but no others
"451 4.4.0 primary target IP address responded with "418.104.22.168 unable to connect."attempted failover to alternate host, but that did not succeed.Either there are no alternate hosts, or delivery failed to all alternate hosts."
We have an Exchange 2010 server and we have not made any changes recently and email flow has been okay otherwise.
The rest of our clients are okay. Is it on their end? Any assistance offered would be greatly appreciated.