Everyone is snickering at this and talking about philosophy, but there is actually a legitimate point being made here, albeit obliquely: how do you explain to a non-technical user that their data has been deleted on the server, but that their client still has a cached copy that they might want to try to salvage somehow? I submit that this is a nontrivial problem worthy of serious consideration.
How about: "This message has been deleted from the mail server, but Outlook still has it in its temporary cache on this device. You can copy the message contents, or discard it from the cache, at which point it will be permanently deleted."