A proof of postage is a document or receipt provided by a postal service or courier when you send a package. It serves as evidence that you have posted an item, showing the date, time, and destination address of the parcel. It typically includes details like the tracking number (if applicable), the weight of the package, and the service used (e.g., tracked mail, express delivery).You should ask for this on posting your return, and retain the receipt until you have received notification that your returned items have been received safely.