The FedEx part is not to avoid the mail fraud charges, it is part of the scam because, if they don't get your check quickly enough, you'll find out that their Money Order is counterfeit and stop payment--

The thing is, if the scam doesn't work, it costs them nothing but postage--they may pull this thing hundreds of times to get a few checks that actually clear--still, it must work, or they wouldn't keep doing it--