It seems we have come to a consensus that the USPS is a rough ridin' joke.
However, the libs on this board clearly have no rough ridin' clue what is contained in the constitution. They also think running the post office is the disastrous manner it is currently operated is acceptable. I could not be less surprised.
I don't know that anyone has taken that stance. But you don't often concern yourself with understanding opposing view points.
As for the Constitution, there is clearly no expressly written mandate. However, there are limited enumerated powers given to Congress and opening post offices, as well as constructing roads expressly for the use of carrying mail, is about as clear a direction as is offered in the Constitution.
I'm as apt as anyone to adding modern context to a Constitution written by people incapable of imagining our current society as they wrote it, but simply taking away postal service seems ill-advised both Constitutionally and in our contemporary context.