Today we're going to discuss the history of the postal service. In the 19th century, letters were delivered by horse-drawn carriages, which was slow and unreliable. It wasn't until the introduction of the railway that mail could be transported quickly across long distances. By the early 20th century, airmail began to emerge, but it was initially only used for urgent documents due to its high cost. Interestingly, the invention of the postage stamp in 1840, known as the Penny Black, revolutionized the system by making prepayment possible, which greatly increased efficiency. However, the real turning point for speed came with the development of automated sorting machines in the 1960s, which reduced processing time dramatically.
❓ According to the lecture, what was the main factor that significantly increased the speed of mail delivery?