I mean, delta.chat exists...

The other way would be a dht of hashed email addresses or hashed keys, but then you could look up live email addresses to send spam to.

The magic of tor v3 is that the plain address record is needed for some time based calculations about the dht record, e.g. they publish the descriptor's of the site using the public key as a reverse lookup

But that wouldn't work to obscure the email or use the email as a lookup because the dht wouldn't have a way to prove the record was true to that email, unless it was sending emails from it

I guess that leaves DNS records or some kind of activity pub system with webfinger