I’m not sure if this belongs in MPSIMS or IMHO. Moderators, move it if necessary, with my apologies and thanks.
We lived with my in-laws for a month last year. We forwarded our mail there, and again when we (gladly) moved out. Now we often get mail intended for them. The address is ours, but the name is theirs. We don’t get bills or important mail, just solicitations from various political activist groups.
I know we may not open someone else’s mail, but it is our address, and the intended recipient has told us they don’t need it.
We strongly oppose what most of these groups stand for. Can I open them, fill out the “survey” with our opinion (which is far from the in-laws’ beliefs) and return it (sans donation) legally? I would never sign MIL’s signature, so I would not tell the group that I am her; I’d just let them assume it.
Since your in-laws have said they don’t want the mail, there’s nothing illegal about opening bulk mail addressed to someone else. The post office won’t forward, and the senders really don’t care. With no donation enclosed, however, the surveys are probably pitched. If the surveys ask for your in-laws names and addresses, the mailings will continue regardless of how you answered the questions because any returns are looked at as possible future donors.
If the intended recipient is OK with you opening mail addressed to them, then it’s OK, end of discussion.
In the US, you would think there would be one law that covers the whole country about whether you may open mail delivered to your address, but someone else’s name. There is. But the federal appellate courts have interpretted it differently in the different circuits and the Supreme Court has declined to resolve the conflict. So the answer depends on where you live.