usps shein refers to the use of USPS as a shipping carrier for orders placed on Shein, a popular online fashion retailer. Shein uses a variety of shipping carriers depending on the location and shipping method selected. USPS is one of the carriers for U.S. customers, with delivery typically taking between 7 to 15 business days, depending on the selected shipping option. Buyers can track their Shein orders using the USPS tracking number once the package is shipped.