Exchange 2010 to 2016 migration problem

PaulH 41 Reputation points

Ultimately we are trying to migrate from Exchange 2010 to Exchange online however we have to use 2016 as a stepping stone.

I have the 2016 server installed and working. I've created a test mailbox on the 2016 server to test mail flow. I can send mail to that mailbox all day but it cannot send out. Looking at the mail queues it shows the error:

4514.4.395 Target host responded with error. -> 451 5.7.3 Cannot achieve Exchange Server authentication

I've created individual receive connectors on each of the two Ex2010 servers just for this particular server with no auth necessary yet I still get this error.

Can anyone help?

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Andy David - MVP 140.8K Reputation points MVP

    Yea, no need to create custom receive connectors. The servers should be able to communicate out of the box. Was anything changed on the default 2010 connector

  2. Aaron Xue-MSFT 2,581 Reputation points Microsoft Vendor

    Hi @PaulH ,

    Agree with Andy. The issue sounds like the receive connector.

    And Exchange need to choose Exchange Server authentication to send internal mail flow.

    Here’s a similar case for you reference.
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  3. PaulH 41 Reputation points

    I'm going to update this but I figured this out. There was another connector for non Exchange/Outlook connections that still had the IP address of the new Ex2016 server on it. Didn't seem to matter that I made the new connector first in the connector list. That old one seemed to have priority and disallowed the connection.

    Thanks for all the help.