The Universal Postal Union is a specialized agency of the United Nations (UN) that coordinates postal policies among member nations and facilitates a uniform worldwide postal system. It comprises 192 member states and is headquartered in Bern, Switzerland.

The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal systems have generally been established as a government monopoly, with a fee on the article prepaid. Proof of payment is usually in the form of an adhesive postage stamp, but a postage meter is also used for bulk mailing.