Physical mail costs money, but 80% of the mail I receive is junk mail that somebody has paid to send me.

Of the 20% of mail that is useful to me, it's still pretty much all just from corporations who have decided to send me a physical letter even though they have my e-mail - e.g. the water company sends me some brochure to somehow justify how much money they're charging by breaking down what they spend all their money on etc...

I get almost zero "real" mail from actual people nowadays. Now it costs £1.80 to post something first class and 91p second class, real mail is basically limited to birthday and Christmas cards. I myself send so few letters, than I still have a couple of stamps in my wallet that I technically bought 6 years ago when they cost 35% the current price (although they were replaced with barcode versions by sending them in to Royal Mail).

Plenty of companies pay the post office to deliver paper spam to my mailbox each day. I don't want any of that, either. "Free" makes spam easier, but a cost doesn't prevent it.

No... but paper spam actually pays less than a regular letter. Make it pay more, and the amount will go down. Not to zero, but down significantly.

The post office _wants_ some spam ads in the mail. They get paid less but everyone gets it. At this time without mail ads there would not be enough mail most days to send a postal carrier out. Think of it as the fiber in your diet. You don't get anything nutritional out of it but it helps move things along.

that is what I was thinking