Oh yeah that is pretty silly. You could make the kingdom's fastest and most people-demanding mail system, but anything more and your DM is just indulging wacky shenanigans. Preservation of momentum and damage by air friction aren't in the book so that's not so much bending RAW as it is quickly switching the PHB for a Physics 101 book and expecting nobody to notice. Bugs Bunny might be impressed but puzzled why you'd bother with those books at that point.