This is by design, because you mailbox is still located on the older Exchange server.
The solution to Access the Exchange Admin Center (Exchange 2016 or 2013) is using the URL like this, appending (?ExchClientVer=15.1):
https://FQDNofTheExchangeServer/ECP?ExchClientVer=15.1
How to Access the Exchange (2013/2016) Admin Cente
原文地址:http://blog.51cto.com/10981246/2104246