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Sebastian TalmonFlag for Germany

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Error 400 BadRequest for some Outlook RpcHttp Proxy Connections through Exchange 2016 to Exchange 2013

Hi,

we are in progress of migrating an Exchange 2013 to Exchange 2016.

Clients are already connecting through the new CAS Server (Exchange 2016) to their Mailbox on Exchange 2013.

Some Clients can not connect to some of the Mailboxes (Offline Mode) - also some clients have connections to shared mailboxes and have problems with only some of them, so not possible to limit it to specific users or outlook clients.


On Exchange 2013 we get the http errors in the log:

C:\Windows\System32\LogFiles\HTTPERR:

2018-10-29 10:00:27 x.x.x.x 19221 x.x.x.x 444 HTTP/1.1 RPC_IN_DATA /rpc/rpcproxy.dll?server.localdomain:6001 400 2 BadRequest MSExchangeRpcProxyAppPool

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On the Exchange 2016 Errors are visible in the HttpProxy RpcHttp Log (<Exchange Server Install Path>\Logging\HttpProxy\RpcHttp)

HttpStatus: 200
BackEndStatus: 200
ErrorCode: InternalServerError      

Method: RPC_OUT_DATA
ProxyAction: Proxy
GenericErrors: StreamProxy=StreamProxy-Response-ExpectReadCallback;PossibleException=IOException;

Versions:
Outlook 2010 connecting through Exchange 2016 CU11 on Windows Server 2016 to Mailboxes on an Exchange 2013 CU20 on Windows Server 2012



Any Idea how to troubleshoot further?

(the Exchange is only available in the local domain, not possible to try testconnectivity.microsoft.com)
Avatar of Sebastian Talmon
Sebastian Talmon
Flag of Germany image

ASKER

Maybe it was a problem with Kerberos Auth - we have now set it to NTLM and can fix it at the moment with remove/add the outlook connection again (so autodiscover will pull the new settings)
2018-10-29 10:00:27 x.x.x.x 19221 x.x.x.x 444 HTTP/1.1 RPC_IN_DATA /rpc/rpcproxy.dll?server.localdomain:6001 400 2 BadRequest MSExchangeRpcProxyAppPool


1- It’s recommended to modify the valid port registry  

2- try to move back these users who is "offline mode" from exchange server 2016 to 2013 , tell me what happens
Do you have DR site?
Thanks for your suggestions

As a quick&dirty workaround we disabled Kerberos Auth, so users can now work again (see my comment above).

I will try your solutions if I am able to enable Kerberos again in the next week, and report back if it was successful
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