We are in the process of replacing Exchange 2013 servers with Exchange 2016. The Exchange 2013 and 2016 servers reside in different AD sites and all mailboxes (user/arbitration/public-folder) are moved over to the 2016 site and are accessible just fine. Exchange powershell administration also just works fine. Also when I logon to the desktop of the Exchange 2016 server and open the https://localhost/ecp web console it works just fine and I use that admin console. However, when I try to open the ECP using the URL https://webmail.domain.com/ecp it always fails with the error:
The Admin accounts that we use don’t have a mailbox and never had, and this issue did not occur when we had just Exchange 2013 servers. The Exchange 2016 version is CU11. The Exchange 2013 servers are not the latest CU but right now I don;t have that detail with me. If it is important I will look it up. I’ll see if enabling a mailbox for my admin account helps but I’d rather be able to run the ECP without that just like it used to work.
This isue is solved now. It was caused by an invalid redirect behavior of the L7 Azure Application Gateway that is configured in front of the CAS servers. The L7 paths and default redirect rule is now reconfigured and /ecp is reachable.