I recently ran into an issue during an Exchange 2010 to 2013 migration where external users could not connect with Outlook externally. Both Exchange servers did not write any errors or warnings to the application logs and the latest service packs and cumulative updates were all applied.
When I ran an Outlook Connectivity test on Test Exchange Connectivity I would get the following error:
Attempting to ping RPC proxy. RPC Proxy can’t be pinged. Additional Details An unexpected network-level exception was encountered. Exception details: Message: The remote server returned an error: (500) Internal Server Error. Type: Microsoft.Exchange.Tools.ExRca.Extensions.MapiTransportException Stack trace: at Microsoft.Exchange.Tools.ExRca.Extensions.MapiRpcTestClient.PingProtocolProxy(String endpointIdentifier) at Microsoft.Exchange.Tools.ExRca.Tests.MapiPingProxyTest.PerformTestReally() Exception details: Message: The remote server returned an error: (500) Internal Server Error. Type: System.Net.WebException Stack trace: at System.Net.HttpWebRequest.GetResponse() at RpcPingLib.RpcPing.PingProxy(String internalServerFqdn, String endpoint) at Microsoft.Exchange.Tools.ExRca.Extensions.MapiRpcTestClient.PingProtocolProxy(String endpointIdentifier) Elapsed Time: 290 ms.
This eventually resulted in a ticket with Microsoft. Support was able to resolve the issue by doing the following:
Ran this PowerShell command on the 2010 server to update the internal Autodiscover URI to point to the 2013 server:
Set-ClientAccessServer -Identity -AutodiscoverServiceInternalUri https://exchange.server.fqdn/Autodiscover/Autodiscover.xml
Changed the “Default AppPool” application pool (IIS) on the 2010 server to use the LocalSystem identity and recycled the app pool.
Hopefully this helps anyone else stuck on a migration.