Home » Exchange Server 2010 » Client Connectivity » RPC through CAS for Mailbox Access: How does it work?

RPC through CAS for Mailbox Access: How does it work?


  • After an Outlook Profile is created, Outlook needs to connect to the Mailbox and AD. Note Outlook 2007 and higher will connect to Autodiscover if it deems the profile needs to be changed.
  • When Outlook launches, it connects to an Endpoint Mapper (EPM) using port 135
  • Outlook 2003 and higher only. I am not covering older Outlook versions as these act differently.
  • Outlook has two other settings: “DS Server” and “Closest GC.” You should note that “Closest GC” is not supported in an Exchange 2010 environment, and “DS Server” is not recommended. Outlook needs to connect to the NSPI directory endpoint on CAS vs. some AD server.  Features that break are delegate / multiple mailbox access for older Outlook clients (2003) and support for archived mailboxes.
  • Outlook queries for Three UUIDs (Universally Unique Identifiers):
  • MS Exchange RPC Client Access Services  (a4f1db00-ca47-1067-b31f-00dd010662da and/or 5261574a-4572-206e-b268-6b199213b4e4) formally assigned to the Exchange Information store in legacy versions of Exchange
  • MS Exchange Address book Service (1544f5e0-613c-11d1-93df-00c04fd7bd09) for the MS Exchange RFR Interface
  • MS Exchange Address book Service(f5cc5a18-4264-101a-8c59-08002b2f8426) for the MS Exchange NSP Interface
  • The MAPI client has knowledge of the needed UUIDs, however it will not know the port number the server is listening on for each of these UUIDs since they are random at startup of the service. 
  • The End Point Mapper returns the listening port number for each of the UUIDs on the CAS server.

More Info :

Praveen Kumar

MCTS | Exchange Server


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