Hi, My mail infrastructure consists of an Exchange 2010 SP1 Mail-Server (Win2k8R2 with roles CAS, Hub, Mailbox) and an Exchange 2010 SP1 Edge-Server (Win2k8R2 with TMG, FPE and Edge role). It is still being tested and as such is not used productively yet. A few weeks ago, everything worked fine, but today I saw that two test-mails which I sent monday are stuck in a queue. Queue Details: Next hopdomain: edgesync - default-first-site-name to internet Type: SMTP-Relay in Active Directory Site to an Edge-Transport-Server 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. If I understand correctly, the error message seems to suggest that I should enable Exchange Server authentication on the Edge Internal Receive Connector, which is currently set to "secured externally", but since this was all set by the TMG/Exchange Mail Wizard, I am hesitant to just change it. Additionally, the list of servers in the Exchange Management Console on the Mail-Server shows the Edge-Server as Version 14.0 (= pre-SP1), the EMC on the Edge himself shows 14.1 as it should be. That can't be correct, I installed the SP1 weeks ago. Could that be connected to the main problem? As far as I understand, Test-EdgeSynchronization and Start-EdgeSynchronization don't show anything suspicious. With regards, Pharao2k

Hi, By default, the Authentication methods for edge receive connector are: Transport Layer Security (TLS) Enable Domain Security (Mutual Auth TLS) Exchange Server authentication Please change the it to the default settings above and restart exchange transport service in both Hub and Edge. Then test to see if the issue persists. Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Thanks Gen Lin-MSFT