Cannot achieve Exchange Server authentication

Wed, 17 Aug 2011 16:49:53 +0000

I was testing outgoing mail flow in my new Exchange 2010 setup, which should go from the CAS Servers to the Edge server in the DMZ.

After configuring the Edge subscription I noticed that outgoing mails got stuck in the queue with the following error:

"451 4.4.0 Primary target IP address responded with: "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."

I verified that name resolution back and forth was ok and that I could communicate on port 25, 50389 and 50636.

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Cannot achieve Exchange Server authentication