This document explains the solution for the error "HTTP 503 Service Unavailable on Calendar Integration with Exchange 2007"
The information in this document is based on testing this feature on CUP 8.5 and Exchange 2007
Since Exchange 2007, Microsoft changed the Outlook Web Access URL from /exchange to /owa, which is the virtual directory that OWA uses to access mailboxes on Exchange 2007 mailbox servers. Cisco Unified Presence, however, always sends SUBSCRIBE requests to the/exchange virtual directory, which is the URL that is still used for WebDAV integration with Exchange 2007. During testing with Exchange Server 2007 (SP1), it has been observed that if you change the http://<server>/exchange URL to redirect to http://<server>/owa URL, an error (HTTP 503 Service Unavailable) displays on the Internet Information Services (IIS) Manager console in Exchange 2007.
The condition occurs when Exchange 2007 SP1 is in use, and the Exchange virtual directory target address is modified to redirect to the default OWA directory for webmail.
Follow the below steps in order to resolve this isuue:-
Step 1 From Administrative Tools, open Internet Information Services.
Step 2 Delete the Microsoft Exchange virtual directory in IIS.
Step 3 Review the warning that displays, and run the recommended cmdlet in the Exchange Management Shell (EMS) :
Step 4 Run this cmdlet in the EMS to ensure that the Exchange virtual directory is set up correctly and to add the directory again in IIS.