401 authentication error testing rpc over http proxy

I'm prepping another server for an exchange 2003 to office365 migration and am getting an error message when running the outlook connectivity test at https://testconnectivity.microsoft.com/.

It passes all tests up to the point where it pings the RPC Proxy.
The error is:

Attempting to ping RPC proxy ourdomain.com.
RPC Proxy can't be pinged.
Additional Details
An unexpected network-level exception was encountered. Exception details:
Message: The remote server returned an error: (401) Unauthorized.
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: (401) Unauthorized.
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: 2683 ms.

The server is SBS 2003.
I have confirmed the RPC over HTTP Proxy is installed.
I have confirmed that the correct domains are added to the correct ports in the ValidPorts registry key (however, it does list 593 as well as 6001-6002 and 6004).
I have confirmed that the "white page" is displayed when I visit https://ourdomain.com/rpc/rpcproxy.dll and log in with user credentials.
Reece DoddsAsked:
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Reece DoddsAuthor Commented:
never mind.  I found that I was using the wrong credentials in the connectivity test.
I was using "user@ourdomain.com" and I actually needed to use "internaldomain.local\user".

It now proceeds past the RPC Proxy ping and fails at:

Attempting to ping the MAPI Mail Store endpoint with identity: ourdomain.com:6001.
       The attempt to ping the endpoint failed.
        Tell me more about this issue and how to resolve it
      Additional Details
The RPC_S_SERVER_UNAVAILABLE error (0x6ba) was thrown by the RPC Runtime process.
Elapsed Time: 4346 ms.

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Reece DoddsAuthor Commented:
again - I found where I was going wrong.
The connectivity test was being tested using the Exchange Server as "ourdomain.com" rather than "mailserver.internaldomain.local".  Changing this and all tests pass fine.

Damn SBS2003.  The other 2003 server I did was configured as a public facing server with no internal domain.

Should I close this question accepting my own comments or delete it?
Reece DoddsAuthor Commented:
self resolved.
accepting answers in case someone else has the same issue.
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