Anytime you have a pre-printed label, there is a tracking number on it. That is all the receipt you need. It is scanned when arriving at the P.O., and you can go on line and track it all the way to it's destination.
Also..you can go on line and put the tracking info in and have the mail carrier pick it up at your next delivery time(at no charge)..because I live in the boondox and can't see my mailbox from the house, I don't like to leave packages down by the road..there is an option for them to pick it up on your porch, or front door, too! Couldn't be easier. The carrier scans it at my porch and it's on it's way.