Microsoft Forefront Unified Access Gateway 2010 (UAG 2010) allows a user to define Inactive session timeout. The Inactive session timeout defines the maximum time a session can be inactive before it times out (see http://technet.microsoft.com/en-us/library/ee406216.aspx). When publishing Microsoft Exchange Outlook Web Access 2010 (OWA 2010) using UAG 2010, the session may stay active even if there is no activity for longer than the value defined in the "Inactive session timeout" field.
The UAG 2010 configuration has a setting for Ignore requests in timeout calculations that contains a list of URLs that are ignored in the calculation of the Inactive Session Timeout settings (see http://technet.microsoft.com/en-us/library/ee406216.aspx#BKMK_Global). When a client issues a request to one of the URLs and methods define in this list that contain a body (like in a POST method), the request will still be counted as active even if it matches the settings in this list. In addition, some URLs are missing from the default list for OWA 2010.
2. After installing SP1, add the following URLs and methods to the Ignore requests in timeout calculations settings for the "Microsoft Exchange Server 2010" application:
UAG; Unified Access Gateway; Timeout; OWA; Outlook Web Access