Exchange 2013-2010 Co-existence: Mail Flow is not working “451 4.4.0”
This is to address an issue where Exchange 2010 queue has messages in retry status to Exchange 2013 with below Error message “451 4.4.0 Primary target IP address responded with: “451 5.7.3 Cannot achieve “Exchange Server authentication”
Mail is not flowing between Exchange 2013 to 2010
Mail is not flowing between Exchange 2010 to 2013
Mail is not flowing within Exchange 2013 different mailboxes
Mail is not flowing to self on Exchange 2013
Sending an email using Telnet working from and to all Exchanges.
Mail is only working within Exchange 2010
Internet mail is flowing to and fro Exchange 2010
No error or ndr
Exchange 2013 queue is empty
Exchange 2010 queue has messages in retry status to Exchange 2013 with below Error message
“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”
Telnet to the Exchange 2013 on port 25
Check the exchange verb. None of the exchange verbs were visible.
Disabled the additional receive connector and restart transport service.
telnet again to the port 25
Run the cmd ehlo
Check the verb.
I would like to see if all exchange verbs starting with X are showing in the screenshot.
In my case we had a same IP range was added in additional connector as the IP of the mailbox server and this connector had only anonymous users and TLS was selected in Security.
I removed he IP range and restarted Microsoft Exchange Transport service and this had started showing my verbs and started the mail flow.
The most import thing to pick up from here is ehlo should show Exchange Verbs. If they are not visible then need to disable the additional connector or remove the changes to the default connector until you see the Exchange verbs.
Also don’t forget to restart Microsoft Exchange Transport Service because your changes will not be applied until you restart Microsoft Exchange Transport Service.
Microsoft MVP | Exchange Server