As a postie, I can just give you my views. Yes, we ARE supposed to deliver to whatever address is on the item, even if we know it;s wrong. As an example of why we should, let's suppose one family is having strife, and one spouse gets something sent to a neighbours' so the other half doesn't see it it .
With me, if I have doubts, I'll deliver it as addressed and wait till it's sent back not known before I post to where I think it should go, but there are examples (say a postcard or junk mail) when I'll just take it to where I know is right.
All this will change in a few years of course when we no longer have postmen. The mail will be sorted from start to finish by machine, and the only bit of human interaction will be the housewife delivering it to make a bit of pin money after she has dropped her kids off at school.