USPS partners with several carriers such as UPS or FedEx, where they pick up a certain package and then transfers it to USPS for the final delivery.
USPS Partner Carriers:
- UPS Mail Innovations
- FedEx SmartPost
- DHL Global Mail
Each of the above services will provide you a different tracking number, other than the one that you get from USPS. Appath will always send the USPS tracking number back to the marketplace, as this will confirm the final delivery.