The Universal Postal Union (UPU), referred to as “UPU” or “PUP”, is an international organization that agrees on international postal affairs. Since July 1, 1978, the UPU has become a specialized agency of the United Nations for international postal affairs. Its headquarters is located in Bern, the capital of Switzerland. Its purpose is to organize and improve international postal services, develop international cooperation in postal affairs, and provide postal technical assistance requested by members within its capacity. The members of the Universal Union (192 at the end of 2016) have certain preferential policies with each other and can enjoy tax exemption policies within the amount prescribed by law. Therefore, it is legal to avoid taxes under certain circumstances.

Cross-border e-commerce companies send goods through the local post of the sending country (region), and then send the goods to the destination country (region) through the Postal Union, and then the destination country (region) postal customs clearance and delivery. This logistics mode has simple customs clearance procedures, a world postal network based on bilateral and multilateral cooperation, and network advantages that other express logistics companies cannot match. It also has a low tax rate and relatively cheap postage. It has become the main logistics mode for many cross-border e-commerce companies to enter overseas markets. However, postal logistics is generally slow and has a high rate of lost items. Therefore, this mode is suitable for small, light, low-cost, and time-sensitive products such as food, textiles, and daily necessities.