In this article we are going to look into few things that we need to consider for coexistence of Exchange Server 2016 with Exchange 2010.

Below are the things that we need to think for Outlook Anywhere, OWA, Active Sync , EWS , ECP

For Outlook Anywhere Coexistence –

In Exchange 2010 – 

Enable Outlook Anywhere on Exchange 2010 servers

Set the IIS authentication to BASIC + NTLM in Exchange 2010

In Exchange 2016 –

If you are doing SSL offload then perform the below

Direct the connections to the Exchange 2016 from your firewall.

Note: If you are having Exchange 2013 then don’t need to make any changes since Exchange 2016 supports up-version of proxy with Exchange 2013 . i.e Exchange 2016 can accept the connections from Exchange 2013 CAS server. Unfortunately we don’t have this functionality with Exchange 2010 coexistence.

Perform the below settings in Exchange 2016

Open EAC – select Outlook Anywhere


Select Basic Authentication


If you don’t select basic then you will get  the below warning message with NTLM. You don’t need to worry if you are doing this in Exchange 2013 coexistence, but for Exchange 2010 it should be only basic.


  Uncheck require SSL in all of the virtual directories if you are doing SSL offload for all of the services.




Exchange 2016 Active Sync virtual directories can proxy to 2010 end point without any issues.

Its similar for OAB, OWA and other virutal directories.

All the above settings is for one site with Exchange 2010 coexistence.

If its the same site it does proxy the 2010 users requests straight to 2010 CAS server.

If you have a different site then 2 scenarios comes into picture according to your setup.

If its is a non-internet facing site with the same URL’s then it does a proxy to CAS server for all the requests of that site.

If it is a internet facing external site with external URL then it does a redirect to that URL.

Have done the same setup in my lab setup with single AD site and so far all setting seems to be working fine.

More to explore on the configuration, features and coexistence. Will keep you posted!!