RPC over HTTP to access e-mail was one of the great features Exchange 2003 introduced. Anyone who has tried to configure this access method before Service Pack 1 knows that it could be a real headache, because you needed to use more than one MMC snap-in and had to make some registry tweaks.
With the release of SP1 for Exchange 2003, most of the configuration it?s just done from the Exchange System Manager because it added a new tab called RPC-HTTP on the Server Properties page. This simple new tab turns out to be a great help and really simplifies the configuration process.
Nevertheless, if you're in a single-server scenario, you may still have to do some registry tweaking. The good news is that Harry Bates has designed a small utility that will allow you to perform all these changes by pressing a couple of buttons: RPCNoFrontEnd.
Recommended reading: Exchange Server 2003 RPC over HTTP Deployment Scenarios