i was just thinking about this. i would collect all mail addressed to "current resident" or something equally vague and every christmas drop it off in front of the post office.
Would you then receive it back in your mailbox? I haven't mailed a letter in years, so I'm not sure junkmail gets stamp-canceled.
They can't add that feature because they already have it.
Not really. The best you can do is opt out of directly mailed advertisements to you, personally. If it's one of those "current resident" things, those get blasted out en masse to every house in an area. You're getting those in your mailbox regardless of how many "do not market" lists you put yourself on.
I'm not affiliated with them but I have been using PaperKarma on my iPhone. I snap a picture of the offending piece of junk mail and they figure out who it's from and submit a request to remove me from the list. Still waiting to see how effective it is but it's very satisfying to get notifications that they correctly identified the spammer and have asked them to remove me from their list.
Where do you think the post office makes most of its money? It's basically a spam operation that subsidizes a useful service.