Marc, from what I read it sounds like your process is to add the besadmin account send as perms after the user has been added to the BES. This will cause a delay because the BES won't see the perms until the next scan of the mailbox. If besadmin has send as before the user is added it should work immediately. I just assigned besadmin send as at the domain for all user objects so I don't have to worry about adding it later. It is really no diferent than before when all mailboxes had the rights.