Definition of "posthorse"

His name was Joe, and he lived at Skroperud in Ullensaker. He built himself a new house there, and he had two or three fat cows and a horse, the like of which was not to be found in the whole parish; the horse was often used as post-horse between Mo and Trogstad, and Joe didn't seem to care much how the beast was used, for fat he was and fat he remained.

1886, Peter Christen Asbjørnsen, translated by H.L. Brækstad, Folk and Fairy Tales, page 262