Exchange - 451 4.4.397 error communicating with target host

Dimm Root 20

Hi All,

We migrated from Exchange 2016 to Exchange 2016.

And for test shutdowned old Exchange server. All work normally for except some mailings to internal users. I see mailings email in queue with delivery type SMTP relay to old Exchange. Last error - 451 4.4.397 Error communicating with target host. -> 421 4.2.1 Unable to connect -> SocketTimedout: Socket error code 10060.

If we turn on the old server, then this mailings will be delivered to users without problems.

Other internal and external emails are sent and delivered normally.

What could be the problem?

Jake Zhang-MSFT 1,235 Reputation points Microsoft Vendor

2024-04-25T10:55:08.7766667+00:00
Hello @Dimm Root,

Based on the information you provided, it appears that you are experiencing mail delivery issues after migrating your Exchange 2016 server. Based on my past experience, I thought there might be a misconfiguration of the internal connectors. I have a few questions to confirm with you:

Is there a problem with the mail flow of some special internal users?

On the old server, have you modified the connector settings or created a new connector. If so, it is recommended that you synchronize the configuration on the new server.
Jake Zhang-MSFT 1,235 Reputation points Microsoft Vendor

2024-04-29T08:30:57.81+00:00

Just circling back to check to see how things are going on with this thread. Should you need more help on this, you can feel free to post back.