We have a Exchange 2007 and 2010 CASHUB co-existing. Right now on the 2007 CASHUB, I'm seeing a "451 5.7.3 Cannot achieve Exchange Server authentication." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.
The 2010 is our main outbound server, I know it's some sort of authentication issues with the receive connectors but not sure how to proceed.