It is little known to the public that most other private entities rely on Postal Service to carry out most of their daily functions. In terms of domestic infrastructure, The companies are not anywhere close to Postal Service. Consider this: In 2011, a survey showed that more than 30% of ground shipments by FedEx were carried out by the Postal Service. Regardless of the competition between them, there is regular partnership as well. Therefore, it goes without saying that the Postal Service is relied upon by the private entities because of its intensive infrastructure. Apart from FedEx, other companies that rely on the Postal Service include DHL and UPS. It is very possible that their zip codes are obtained from the much loathed corporation.