Sounds like a dream, really. And you could always have it be user-driven action, like "Copy this line and paste it into your email provider's whitelist", framing it as a positive win for the user since they have total control over who is allowed to communicate with them.

Seems like you could easily do this yourself with a couple of rules in your email client.

I do want arbitrary people to reach out to me regarding my home page, so any just-allow-whitelisted-messages proposals are useless in that regard.

And in practice some minimal address obfuscation has been enough to block any address harvesters, and setting up a contact form or something comparable (and I guess especially also subsequently keeping it spam-free!) would have been much more of a hassle.

Yeah, I feel to that is a much better system. You could have a “grey”list postbox that uses a one time code for that company.

Say you enter a form at a company,and in the message box you just leave that code so they can mail you.