I suspect the Government had secure Blackberries with their own secure backup system. Mail takes up very little space by the way.
Yes the government does have encrypted BBs, but I have never seen or heard of using backups for phones. The emails would be saved on the email server, so what on earth would they need to backup their phone’s data for. Furthermore, classified emails cannot be transmitted or stored on mobile devices such as a BB. It is stated in part of the training courses they take when you get a clearance. Anyone doing so is violated several federal statutes on handling classified material.