Topic Last Modified: 2005-04-26

There are several benefits to using RPC over HTTP to enable Microsoft® Office Outlook® 2003 clients to access Microsoft Exchange Server, instead of using a virtual private network (VPN). The benefits are the following:

• You can use the same URL and namespace that you use for Microsoft Office Outlook Web Access for Exchange Server 2003, Exchange ActiveSync®, and Microsoft Outlook Mobile Access.
  
• You can use the same Secure Sockets Layer (SSL) server certificate that you use for Outlook Web Access, Exchange ActiveSync, and Outlook Mobile Access.
  
• No unauthenticated requests from Outlook can access Exchange servers.
  
• Clients must trust server certificates, and certificates must be valid.
  

You must allow only port 443 through your firewall, because Outlook requests use HTTP over SSL. If you already use Outlook Web Access with SSL, Exchange ActiveSync with SSL, or Outlook Mobile Access with SSL, you do not have to open any additional ports from the Internet.