So instead, there’s no verification mail and it’s the next message, the one that you actually wanted, that gets blocked or sent to spam.

The “privacy advantage” that the issuer can’t learn the identity of the application that wants to send mail seems to me to be a significant functional liability. If it instead produced a token that said to the email service provider “see, the message was invited”, now that would be useful. (It would raise concerns of its own, but it would at least be useful.)