(Hope I'm not wasting your time with this...don't know how many people even know how the mail was delivered in "the old days".)
As a point of interest, the olive drab mailbox shown near the beginning of the vid is a "swing" box.
I was a substitute mail carrier in the summer 1966 and then these boxes were standard. All postman carried a universal key to them on a small chain attached to their belt.
You didn't carry all the mail for your route when you left the PO, just that needed for the first few swings.
Other postal workers in trucks delivered your other mail to certain "swing" boxes. As you finished each swing, you might go back to the box a few times, or go to another swing box, and thus finish your route.
Now with the use of those funky little postal trucks, carrying their swings with them in the trucks, I doubt there's much use for them anymore...even in cities. Maybe they do use them in cities, but I haven't seen one in years.
They're obsolete...and thus the DemonRat story, as always, is a fucking lie.