I still pause to reflect when I see USPS trucks out on Sunday. They probably get double time on Sundays.
During the my 38 years at USPS it was +10% Sunday premium.
Amazon just opened a sortation facility in my hometown. I just about had a heart attack the first time a USPS truck drove into my yard on Sunday to deliver an Amazon package. I have not had a late delivery since the opened that facility.
The carriers on Sunday are “Carrier Associates” be they city carriers, or rural carriers. I don’t know about the rural side, but the City Carrier Associates make about $12 per hour, and 10% differential for working on Sunday. These are not the regular career carriers who are part of your neighborhood...we don’t do Sundays.