I’ve worked for USPS for ~8 months. It’s not just a Sundays thing. I’ve never seen someone else load for someone intentionally. A couple times someone has loaded, then gotten sick or gotten bad news and had to leave. The clerks will sort all the incoming to each route that it goes to, but once it’s in the bin for your route it’s your problem going forward.
I’ve worked for USPS for ~8 months. It’s not just a Sundays thing. I’ve never seen someone else load for someone intentionally. A couple times someone has loaded, then gotten sick or gotten bad news and had to leave. The clerks will sort all the incoming to each route that it goes to, but once it’s in the bin for your route it’s your problem going forward.