[pontifier]

I was working on a system like this years ago. I called it choicelist, and submitted a paper to the FTC spam forum.

It was a user configurable white list solution in which an entity can specify all the ways they may contact you (numbers, addresses, and optionally signing or encryption public keys), and you can white list the organization as a whole.

Messages purporting to come from one of these organizations that fails the self specified check can be safely ignored.

At the time, blockchains didn't exist, and the missing piece of the puzzle was a distributed database not controlled by any central organization.