> The unknown request will be buried in spam - a problem we have already, but worse.

Keep in mind that many people around the world already use this solution.

In my case, I give senders a mechanism to go into my inbox without my explicit approval. The server sends them an email with a URL. They follow the instructions, and their email gets whitelisted.

https://blog.nawaz.org/posts/2018/Sep/solving-my-email-probl...