Symptoms
Assume that you have multiple Active Directory (AD) sites in a Microsoft Exchange Server 2016 environment. Then you configure the Active Directory sites by using the same external URL for the Exchange Control Panel (ECP). When you try to log on the ECP by using a mailbox that's located in a different site, the ECP redirection is failed.
Cause
This issue happens because 302 redirection response contains an incorrect path so that Exchange Server can't understand where it has to be redirected.
Resolution
For Exchange Server 2016, install Cumulative Update 9 or a later cumulative update for Exchange Server 2016.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology that Microsoft uses to describe software updates.
