Newly added Exchange 2016 server in an existing Exchange 2010 hybrid setup - mail flow issues

Regular Contributor

Hi All


Need some help urgently. I just added a new Exchange 2016 server to our existing Exchange 2010 Hybrid setup. For some reason the Exchange 2016 server now wants to participate in mail flow and it can't which is causing the queues to build.


on the queue viewer of the exchange 2016 server the queue is now building. i made no changes to mail flow in the organization.


Getting cannot 451 5.7.3 Cannot achieve Exchange Server authentication.


Any ideas??





1 Reply

I figured this out. 


This article pointed me in the right direction:


Turns out on the Exchange 2010 server there was a receive connector for anonymous relaying that had the IP of the Exchange 2016 server and on this receive connector "Exchange Server Authentication" was unchecked.