Neither snow nor rain nor heat nor gloom of night stays these couriers of justice from the swift completion of their appointed rounds

I have no idea how historically accurate this is, but Patrick O'Brian has a scene in one of his Aubrey/Maturin books where they joke about putting POST PAID on cannonballs. Because it is a death-penalty offense to stop the mail, "[a]nd indeed the man who stops a cannon-ball is unlikely to survive."