"The Name Could Not Be Resolved" Error Message When You Add Additional Mailboxes to Your Outlook Profile
(but I dont think, this applies here)
Try, if its a problem of the user:
go to a different machine, where outlook is installed.
logon as the besadmin account.
setup outlook for the besadmin account.
does that work ?
if your besadmin account has no exchange mailbox, create one, wait, until the Receipient update has been completed or manually force the update on the exchange server. Again try to setup outlook on a workstation with the besadmin account. Then, make a new try on the BES server.
if your besadmin is hidden from the GAL, unhide it.