The issue is that spammers will just have someone who is not a post officer deliver their spam. There was a similar method for email spam, hashcash where you n

The issue is that spammers will just have someone who is not a post officer deliver their spam. There was a similar method for email spam, hashcash where you needed to include some string derived from the message and recipient and some random characters you choose such that it will gag to some number with some amount of 0s at the start. Like bitcoin, the idea was that the cost of computing all the hashes would be prohibitive for mass spamming. It never caught on and I guess webmail would have been more expensive to set up if it had. A system I would like would be one where there is a mechanism to return post if you don’t want it (rather than if it was sent to the wrong address) and the sender must cover the cost of recycling the material and some extra fee to make them not want their post to be unwanted. This would have to apply regardless of how the post was delivered.