I would like an email service where, when someone wants to send me an email, they have to first get some hash, e.g., "{hash}.myaccount@myprovider.com".

Then, in order to get the hash, they have to paypal me 20 cents.

If my attention is not worth 20 cents to them, then they should not be contacting me in the first place.

Further replies to the same thread should be free for some period of time (e.g. a month or so).