[miohtama]

Spam is tradegy of commons, because spammers get infinite free messages. Make message gateways or users themselves to pay the cost, similar to SMS delivery, and the problem is greatly reduced. The cost of low quality marketing becomes unbearable to the spammers, as generally nobody buys their shit.

It does not need to be proof-of-work payment, or even a cryptocurrency payment. Gateways can have peering agreement with each other paid in dollar.