My first thought?
"What a hack!"
Think about it... all of possibly 40 words handwritten on a piece of paper that has been sent around the world with not a tear or a rip. No smudged ink, no foot prints.
The amount of energy spent on pushing this piece of paper is amazing when you think about it. A piece of email would have reached its destination much faster with far more reliability of transport and comprehension (thankfully the hand print it legible!).
My Spam Box, aka my mail box, is stuffed with junk mail. I am on the "Do Not Send" lists but junk mail continues to arrive daily. I've wondered if I could get my point across by just installing a paper shredder. Last year we had bees for a bit and the post office refused to deliver our email... and the problem with this was? (ok, others that live with me would strongly disagree with me on this).
Someone a hundred years from now, maybe as close as twenty, is going to look back at this time in our history and wonder how this ever worked.
It barely seems a step above horse back riders taking messages across the US a hundred or so years ago.
If an engineer noticed a similar system, one as Rube Goldberg'ish as the postal system, in any design, they would remove it quickly.
Too many moving parts, too expensive to maintain.
The biggest problem I see with moving to an all digital environment?
My dog won't get her daily "go nuts at the door because the mailman is here."
She will just have to live with Squirrels.