Exchange 2016 Mailbox Servers Showing in Exchange 2010 CAS Arrays

BYS used Ask the Experts™
We are currently in a state of coexistence with Exchange 2010 and Exchange 2016. Just noticed that the Exchange 2016 mailbox servers are members of the CAS Arrays that were created for Exchange 2010. The Exchange 2016 servers are at least part of the CAS Arrays tied to the respective AD site but wanted to confirm this is expected behavior.
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EE Solution Guide - Technical Dept Head
Most Valuable Expert 2017
Hi Ben,
When you install new Exchange2013/2016 server to an existing Exchange 2010 environment the new server will be added to CAS array by default and your client interface will be the new server. i.e. in your case Exchange2016.
The connection end-point during coexistence should be the highest Exchange version in the organization, that's MS recommendation.
E ATech Lead
Have you followed Microsoft Exchange Server Deployment Assistant ?

Try this:

Point to Exchange 2016, with DAG IP or A record in DNS which resolves to either Exchange 2016 servers. Adjust URLs for the Exchange 2010 environment to have Exchange 2016 proxy access to mailbox servers.

Get complete overview on client connectivity in an Exchange 2016 coexistence environment with Exchange 2010:

Exchange Server 2016 in co-existence with Exchange 2010:

Hope this helps!

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