Cab mail

You're referring to the Cab Mail service!

Cab Mail is a postal service that was introduced in the United Kingdom in 1840, allowing people to send letters and packages through a network of horse-drawn carriages, also known as "cabs." This service was an innovation in its time, as it provided a faster and more reliable way to send mail than traditional horseback riders or foot messengers.

Here's how it worked:

1. Letters and packages were collected from post offices and sorted at central hubs.
2. The sorted mail was then loaded onto horse-drawn carriages, which were specifically designed for this purpose.
3. The carriages, also known as "cabs," would travel along designated routes, carrying the mail to its destination.
4. The mail was delivered to post offices along the way, where it was sorted and forwarded to its final destination.

Cab Mail played a significant role in the development of the British postal system, as it helped to increase the speed and efficiency of mail delivery. The service was eventually replaced by motorized vehicles and modern postal systems, but it remains an important part of postal history.