[MysticLlama]

Often if you can get onto the mailserver and have admin access you can run an app called exmerge. This will allow you to export the mailbox to a .pst file and look at it offline.

This doesn't raise any flags on the account itself since you aren't connecting directly to the mailbox.

A backup to pst can also be done through Outlook, but if he's remotely decent at IT he won't leave his machine logged in and unlocked overnight.