As described on the Outlook MAPI connection to Exchange 2010 CAS fails through UAG 2010 direct access tunnel article, maybe the Outlook connectivity to the Exchange 2010 server could have some troubles through a DirectAccess gateway located on Forefront UAG.
In this article the problem come from Forefront TMG which denies the RPC traffic. However on a deployment I got a similar behavior but something else made this.
1/ Description of the scenarioCustomer needs:
- The branch office should connect to the head office through DirectAccess
- The branch office must use DirectAccess to access to the mail infrastructure
- Outlook use the MAPI protocol in order to connect to the Exchange servers
- The client doesn't use RPC over HTTP