For redundancy we have setup an additional AD site. I have installed CAS servers and while testing connectivity, I notice things fail and am provided with the following event log error & solution: User was prevented connecting to mailbox because the mailbox server resides in a different AD site than the CAS server. Either arrange for the CAS and the MBX server to reside in the same site, or change the configuration setting of AllowCrossSiteSessions to true. I love the solution to change the configuration of AllowCrossSiteSessions to true, sounds exactly what I need. However, I have no clue how this is done? Searching everywhere and there is nothing?!?

With Microsoft PSS the solution is in: C:\Program Files\Microsoft\Exchange Server\ClientAccess\PopImap Open the microsoft.exchange.pop3.exe.config, search for 'allow' and change value to true. Do this also with the IMAP config file, restart services and solves this problem. Dissappointing there is an Event ID with a solution they dont tell you how to solve.