Well, if you were creating a system from 0, you could do that, make it so all npubs could only send so much. But nostr already exists, I can't alter THEIR clients but perhaps I can alter mine to require such. It would probably be on the client level and not need any protocol change, just when you attempt to send something a invoice would pop up at an amount you set
Discussion
But if they weren't using the same client, how would the invoice pop up?
Ok. You send your dm.
My client auto replies with an invoice.
You pay
Then I get the message.
Since it happens through DMs, it should work no matter what client you have
Oh! I was talking about spams. I am obsessed lately. Sorry! Relays can slow DM'ers down.
A client-client thing can also be done like hashcash, yes.
Never thought about invoices but as far as I remember similar things occured outside nostr like "If you want to talk to me pay this invoice and choose a time slot".
Yeah, this is just be a nostr dm spam filter.
Thanks for being obsessed with this. I'm worried about spam. Email made the web what it is. A decentralized open system to exchange ideas and information. However, it's collapsed into a centralized reality of major operators. Not only due to spam but as mentioned in this thread, running an email server today is not really possible because everyone thinks you're spam, and you have no way to prove otherwise.
I actually run an email server. It is not that bad. A few times it went to spam folders of others.
I think in the future, when just starting users will need to gain reputation. During this phase the messages and pubkeys can be expensive. After reputation is built, messages (events) can be much cheaper or even free..
Some relays can be strict, then users can go to smaller relays to build reputation. Once the user acts well in the network (i.e. no spamming etc) then big relays can accept the events without PoW.