I once when I lived in a rural area, with a small PO received a despicable scam focusing on elders, containing a return-postage-guaranteed envelope. The postmistress couldn't provide direct instructions, but enough for me to surmise that anything I could actually fit in the envelope would work.
I filled it as full as possible with thin lead sheet (often used for flashing around chimney-roof intersections), a bit of reinforcing clear packing tape around the edges, and a nasty note. When I brought it back for mailing, I got a bit of a smile and assurance that it would go properly.
Satisfying, and if everyone did it...
Better to make sure the company gets it so they have to pay someone to open it.
Do you have a source for this? What do they do with it then?
The only ("only") problem I personally have is that it generates soooo much waste. It is always so frustrating checking the mail, and immediately dropping 10 or so sheets of paper in the trash before I even close the mailbox (the safeway mailer is especially bad at this...)