You want to enable RPC tunneling over HTTPS so that your Outlook 2003 users can use Outlook directly against your servers.
Setting up RPC over HTTPS is easier in Exchange Server 2003 SP1 than it was in the original release version, but it's still a reasonably involved task that requires you to know a good bit about your Exchange topology, and to understand the underlying mechanics. There are three basic steps:
Setting up an RPC-over-HTTP proxy. This step requires a Windows Server 2003 computer, on which the proxy runs; the proxy's job is to disassemble incoming HTTP packets that contain RPC traffic and convert them into conventional RPC traffic, then reverse the process for reply packets.
Configuring the Exchange front-end servers. This process is very simple, requiring nothing more than clicking a radio button; however, it must be done separately for each Exchange FE.
Configuring the Exchange back-end servers. This is also a matter of a single click of a radio button.
To install the RPC-over-HTTP proxy, do the following:
Log in to the front-end server using an account with Windows administrative privileges.
From the Control Panel, open the Add or Remove Programs applet.
Click Add/Remove Windows Components.
Select Networking Services and click the Details button.
Ensure that the RPC over HTTP Proxy box is checked and click OK.
Click Next (you may need to pop in your Windows Server 2003 CD during the install ...