I configured RPC over HTTP but the Outlook client couldn’t connect

I configured RPC over HTTP on an Exchange Server 2003, but the Outlook client couldn’t connect. For troubleshooting try accessing RPC by browsing:

https://servername/rpc

If you successfully authenticate and RPC over HTTP is running, you will get the message:

HTTP Error 403.2 - Forbidden: Read access is denied

RPC over HTTP requires, on the client side (Windows XP Service Pack 1), the hotfix KB331320. Next, when you configure the e‑mail profile, going to Exchange Server Settings → Connection → Exchange over the Internet → Exchange Proxy Settings. In Connection settings, type the URL of the RPC proxy server. Then select “Connect using SSL only. ”Next, in “Mutually authenticate the session when connecting with SSL,” type “MSSTD:Public_FQDN_of_Server.” And in “Use this authentication when connecting to my proxy server for Exchange,” select Basic Authentication. You can test the settings using the RPCDump tool to check whether the server is listening on ports 6001, 6002, and 6004. If not, in the following Registry path:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTDS\Parameters

add value

NSPI interface protocol sequences=ncacn_http:6004

You can then view real‑time connection information by running Outlook with the following parameter:

outlook.exe /rpcdiag

This is described in the Knowledge Base article KB827330.