Here's how the word evolved:
* Latin: *posta* (post, station)
* Medieval Latin: *posta* (post, station)
* French: *poste* (post, mail)
* English: *post* (mail, position)
The concept of "posta" originally referred to a relay station for horses and riders, used for rapid communication and transportation. This system evolved into the modern postal service, which we know today.
Therefore, the word "postal" essentially means "relating to the post or mail".