Just because MS says Exchange 2010 uses the CAS for MAPI communications doesn't mean this is always the case

I recently had to upgrade to Exchange 2010 sp1 in a complex environment. I thought that as tech-net states http://technet.microsoft.com/en-us/library/ee332317.aspx outlook clients with Exchange 2010 mailboxes will always use the CAS server to communicate via MAPI (Mail RPC) traffic. In our case we found outlook communicating with the Mailbox servers directly. Specifically mailboxes servers with public folder databases. I suspect that there is a great deal that occurs with Exchange that Microsoft never publishes.