Field Notes: Exchange 2010 Coexistence and URL Redirection Mayhem

During a recent deployment of Exchange 2010 I ran into a rather challenging issue. This deployment involved maintaining a solid coexistence with a legacy Exchange 2003 deployment. After updating DNS records to route traffic to the Exchange 2010 CAS server(s) and configuring URL redirection using the method described in the MS TechNet article Simplifying the Outlook Web App URL (modified date: 2010-04-19) connections to the <CASArrayURL>\Exchange were receiving an IIS error (see Symptoms).

The project required that we maintain this URL functionality because users were both familiar with this URL and many had shortcuts that referenced this location.

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