Let us now look at the costing of the mails. The United States Postal System uses a prepaid method of payment. The charge is always fixed, and it is evident by the stamp affixed to the mail item. The exact amount depends on the type of delivered item, delivery requirements, and weight. It also important to note that improper postage will be returned to the sender if the postal office cannot deliver it going by the addresses. If the UPSS cannot determine the exact destination of the mail item through the ZIP codes and addresses, then it has to be returned.