Short answers, pulled from the story.
Mail, also called post, is a system for physically transporting postcards, letters, and parcels from one place to another. Since the mid-19th century national postal systems have generally been government monopolies, with a fee on the article prepaid, usually shown by an adhesive postage stamp. The modern business model breaks into four stages: collection, sorting, transportation, and delivery.
The Greek historian Xenophon credited the Persian king Cyrus the Great with inventing a real postal system around 550 BCE, ordering every province to organize delivery of post to its citizens. The earliest documented organized courier service, however, was in Egypt around 2400 BCE, where Pharaohs sent couriers to spread decrees. The earliest surviving piece of mail is Egyptian and dates to 255 BCE.
The Universal Postal Union, or UPU, was established in 1874 and includes 192 member countries. It sets the rules for international mail exchanges and operates as a Specialized Agency of the United Nations, setting international postage rates and defining standards for postage stamps.
By the end of Kublai Khan's rule there were more than 1,400 postal stations in China alone. These stations had about 50,000 horses, 1,400 oxen, 6,700 mules, 400 carts, 6,000 boats, more than 200 dogs, and 1,150 sheep at their disposal. The system, called the Ortoo, was installed by Genghis Khan and remained operational into the 18th century.
Sir Rowland Hill reformed the United Kingdom postal system based on penny postage and prepayment before 1840. His proposal for pre-printed envelopes and adhesive stamps led to the invention of the postage stamp, the Penny Black. Before this reform, recipients paid for letters based on distance and the number of sheets of paper.
Paper mail is declining because email and social networking sites became fierce competitors, earning physical mail the retronym snail mail. The volume sent through the U.S. Postal Service has dropped more than 15 percent since peaking at 213 billion pieces a year in 2006. Continued drops led PostNord to stop delivering letters in Denmark at the end of 2025 and remove street mailboxes.