I agree that's the answer. Unfortunately many services out there (including Netflix apparently) don't do that.

You’re not missing anything, but if gmail delivers all the mail, and I just trash it, we’ve fixed the symptoms, but not the problem, and we’ve made the problem invisible.

I agree that sending verification emails should be the standard. But if I can’t bounce the emails then there isn’t even the slightest way to inform the sending service that there might be a problem.