Pneumatic mail, also known as underground mail, stands as one of the oldest methods of mail and document delivery. This system operates on the principle of a network of airless tubes of specific diameters, thereby eliminating air resistance. Capsules carrying documents are propelled through these tubes using compressed or rarefied air.

1. The foundational principles of pneumatic mail were first outlined in the works of the engineer Hero of Alexandria. His first-century innovations laid the groundwork for the development of pneumatic mail.

2. In the futuristic animated series “Futurama,“ pneumatic mail is used extensively for transporting people on Earth in the year 3000.

3. By the mid-19th century, pneumatic mail was actively used for delivering letters and documentation, including telegrams, in major cities across various countries, starting with London and subsequently expanding to Vienna, Berlin, and Paris.

4. In Italy, special postage stamps were issued to pay for pneumatic mail services, while in France, Germany, Austria, Czechoslovakia, Argentina, Algeria, and other countries, various postal items like envelopes, postcards, and seals were used. These items, along with corresponding stamps and labels, have become collectibles and subjects of philatelic study.

5. The ANТ-20 “Maxim Gorky“ airplane was equipped with a pneumatic mail system.

6. Prague was the last city to operate a pneumatic mail system, which ceased operation in 2002.

7. Pneumatic mail has become a prominent feature of the steampunk genre, alongside steam engines, typewriters, dirigibles, and telegraphs.

8. In contemporary life, pneumatic mail continues to be used, notably in libraries, banking, and medical facilities, where rapid delivery of important documents is essential.