So every time I type my email somewhere, I also have to go to my mail provider and pre-emptively whitelist the sender? This does not sound like a very good UX.

So every time I type my email somewhere, I also have to go to my mail provider and pre-emptively whitelist the sender? This does not sound like a very good UX. I suppose you can have a special system where you have a browser plugin which automatically generates some sort of subscription token and pastes it alongside email into subscription form.. but this will need cooperation from every mail-sending app, and will not handle non-web uses cases at all...