Why is mail called “mail”?

The word comes from the Old French “male,” meaning a bag or pack — originally referring to the actual sack used to carry letters and parcels on horseback. Over time, “mail” shifted from meaning the bag itself to meaning the letters carried inside it. That’s also why we still say things like “the mail is here” instead of “the mail bag is here” — the word evolved with the object it used to describe.