What heppne to:
“Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of
their appointed rounds”
It is hard to deliver the mail if the governors of some states close down the roads due to black ice, white outs etc.
The story on that - “Neither rain nor snow nor gloom of night . . . “ is not their official mission statement. The motto was chiseled or engraved on a building owned by a private courier service, before the Post Office took it over, something like that.
So it ain’t theirs, I guess, even though it has been attributed to them.