I was having a thought the other day about how much spam mail I get in my USPS mailbox. I wish we could tell USPS to return letters if they don't meet a customer-specified proof of work, much like the idea of filtering out messages on nostr that don't attach some degree of proof of work.

This could come in the form of sats, or simply just putting more stamps on the letter. It's a win-win. You get less spam, and USPS gets more funding.