The W.H. isn't stupid enough to let anything that incriminates B.O. to leave the oval-office.
I'm sure he has IT-guys who's kung-fu is strong, when it comes to covering cyber-tracks, and in an instant, he can erase any and all emails pertaining to a particular topic.
Then again, if his IT-guys are strong, there's always someone who's kung-fu is STRONGER or better, and they'll dig until they find what they're looking for.