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I would like to see a time where a private messaging service could be such that the receiver can put his threshold to how much a person needs to send for said receiver to read it. Charging could be optional based on whether something is determined to be "spam" or not.

there was some idea of cryptocurrency about that u spoke they use it to mail, so if sender want to be in inbox of user he need to pay crypto

Yes in fact these spammers often deliberately make sure that they make few actual posts so they can't get flagged for their crappy behaviour.