1: The Bes server gets the information from their person document. So in this case it's gonna be server B.
The bes server on Domino A is gonna poll (using a connection doc) every user's mail db's on server B. It read and write informations and send it back to RIM Network via an internet connection.
You can read a technical overview here:
http://na.blackberry.com/eng/deliver...iew%5B1%5D.pdf
Mike