I was getting a lot of spam letters so I bought a stamp and started stamping everything I didn't want.
I would drop the stamped letters at the postoffice (not in my own mailbox)
This went on for a few months and I get much less spam now. 
I'm think every time it is sent the company that paid the original postage gets charged again.
Genious
Great stamp!
I used to just write RTS on the envelope & stick it in a post office box.
Sometimes they were addressed to me & sometimes they were the previous occupant. After a while they do stop coming.
There was a comedian (maybe Jerry Seinfeld) that used to advocate for sending junk mail from one company to another using the included prepaid envelopes that they send you to respond or whatever.
