Yes, its possible and its not a feature but a big security bug in the iPhone OS 3.0. Apparently the Spotlight search doesn’t sync its cache with the current status of your emails. So if, you remember the subject line of a deleted email message, it still shows up on the spotlight search. And with some persistent try it actually pulls out the message content aswell and displays the text. ‘
The bug as it seems lets you pull out emails as old as a few months! Video below shows the whole thing demoed in detail: