By default, Microsoft Outlook 2003, 2007 and 2010 connect through port 443 for RPC over HTTPS. This cannot be changed inside of Outlook 2003, 2007 or 2010 and must be changed via the registry. If you attempt to change the port number in Microsoft Outlook 2003, 2007 or 2010, the following message will be displayed:
“The proxy server you have specified is invalid. Correct it and try again.”
In essence, Microsoft Outlook 2003, 2007 and 2010 has HTTP and HTTPS hard coded to TCP ports 80 and 443.
Recently, we had a client who had set their OWA to listen on TCP Port 446. Works fine in browsers / Smart-Devices but is a different situation for Microsoft Outlook. Using a VPN is an “easy alternative” but is more of a nuisance if out and about all the time.
Imagine you want to move your Outlook Web Access to a different port (security reasons? Or maybe just that another application is hard coded to port 443…)
The following method is unsupported by Microsoft, please use it at your own risk. Editing the registry is required.