In the last part of my fun Exchange 2003 deployment I wanted to enable RPC over HTTP for Outlook 2003's VPNless Exchange connection. Was actually quite easy, heres the process (for a single server Exchange deployment with no front ends)

1. Highly recommend you use ISA to front end it. As I mentioned in previous posts I used ISA's reverse proxy function to terminate a secure SSL channel at the ISA Server and then recreate another one separately to Exchange...why? primary reason is security. Secondary reason is that you can use OWA forms based logon with SSL and use the great compression functions that it now has.

2. You need Windows Server 2003 DCs and GCs in order for it to work. Also Exchange 2003 must be running on Windows Server 2003. Patch both the Windows Server install and get Exchange 2003 SP1 on aswell.

3. Install the RPC over HTTP service on the Exchange Server from Add/Remove programs.

4. Follow Q article 833401. If you have deployed Exchange 2003 SP1 it makes it a lot easier and you wont need to type as much in in terms of the registry settings that are required. You will need to add a registry setting to each GC though that Exchange will be accessing.

Test it by going to the https://mail.servername.com/rpc and authenticating. If it comes back and says "HTTP Error 403.2 - Forbidden: Read access is denied" then youve done everything right! :)

5. You need to configure your Outlook clients to use it as an option. You configure it in your email settings/Exchange Server settings, then the Connections tab and finally Exchange Proxy settings. You can just fill in the FQDN of your mail server thats being reverse proxied and if you want the next level of security to mutually authenticate then you need to put that in aswell. Tick the "On Slow networks connect using HTTP first then TCP/IP" and choose basic text authentication. Obviously, because you're using SSL to encrypt the channel your basic text credentials wont be compromised.

The client computer must be running Microsoft Windows XP Professional Service Pack 1 (SP1), and the update package that is described in the following Microsoft Knowledge Base article must be installed:

331320 Outlook 2003 performs slowly or stops responding when connected to Exchange Server 2003 through HTTP.
Note: The update package that is described in article 331320 is included in Microsoft Windows XP Professional Service Pack 2 (SP2). If you have installed Windows XP SP2, you do not have to install the update package that is described in article 331320.

Enjoy!