If a Census worker asks you for information about a particular household on your route, what are you authorized to tell them?
Not a mail carrier, but I can find no obligation or duty of confidentiality to residents that mail carriers are required to uphold. There are plenty of regulations that all employees of the USPS are bound to keep confidential the intellectual property and knowledge of the inner workings of the USPS.
If anecdotal evidence is of any use, our mail carrier at our previous residence was a gossip hound. She loved to dish the dirt on our neighbors to my wife. Who was getting divorced, who was recently laid off, who had a boyfriend move in, who bought a new car recently, etc. etc.
Don’t know how much this blossomed but there were plans to consider having mail carriers be census takers:
why would census worker ask mail carrier rather than resident?
To get information if the respondent is unavailable or refuses to answer.
There’s rules for that of course (was in the back office for part of the '10 census). IIRC, the order is something like ask person who answers the door, try to call the address, repeat that loop a couple times. Then various forms of educated guess, including checking the white pages and various public databases. You probably could get authorization to talk to a postal worker because federal employee, but not sure how common.
And then you have to take into account the rechecks, either random or “this census taker’s data looks like they wrote entries at random while sitting in McDonalds”
Good luck finding one if it’s raining: Seinfeld - i dont work in the rain - YouTube