[dancing_shark]

In general, USPS does have the infrastructure to do this: Managed Service Points are barcodes placed on mailboxes that can be scanned by the carrier, to establish when he/she reaches certain checkpoints.

https://about.usps.com/strategic-planning/cs02/2f3.htm

It's a more modern version of the mechanical "watchclocks" installed in buildings to ensure that guards make their appointed rounds. https://en.m.wikipedia.org/wiki/Guard_tour_patrol_system https://en.m.wikipedia.org/wiki/Watchclock

I have no idea how regularly USPS examines or audits their MSP data.