Interestingly enough, stagecoaches are called "Postkutsche" in German-speaking countries (because they also carried mail), and Switzerland's regional buses ("PostBus") are still operated by a subsidiary of the Swiss Post: https://en.wikipedia.org/wiki/PostBus_Switzerland. So some ideas live longer than you might expect...

Something similar also exists in Austria and is still called "Postbus", although it's been operated by the national railway company since 2003.