> If you didn't want to read them, you wouldn't have signed up.
There are many use cases beyond what you're stating. Often I need to sign up for a web site temporarily ("Sign up to get our free ebook!") ("You need to sign up to place an order") In those cases I simply ignore the emails.
If I sign up for a newsletter with the intention of reading it, I'll keep an eye out for it and whitelist it. It's not hard.
> Your quarantine will be full (even more than "Spam"), and you won't know (necessarily) what the from address looks like.
I've been using this system for 3-4 years now, and this so far has not been a problem. I still monitor the quarantine folder as I don't expect everyone to go through the hoops to get to me. It's just a much smaller burden than having it all show up in the inbox and I can check it at a different pace (e.g. once every few days).
And even if I somehow forget to whitelist your site, what's the worst that will happen? I won't get messages from your site. Of all my worries in this world, this just doesn't even register.