The United States Postal Service has various mail classes and services for different types of needs and requirements. Mailing; Collect on Delivery; USPS Tracking;. Your Tracking Number may be found on several different items like receipts and Redelivery forms. This FAQ explains the different ways you as a sender or recipient can find the tracking number of a mailpiece. After Mailing an Item, Can I Request a Return Receipt? Return Receipt must be purchased at the time of mailing.