This is why I usually hit the Report Spam button. Sometimes I'll receive a legit looking email that I plausibly signed up for but don't remember - I could follow the unsubscribe link/hit unsubscribe and be a good citizen, but at that point the safer thing to do is to not interact with the mail and let Gmail know I don't want this anymore.

I'd rather receive the mail and let Gmail put it into a blackhole than try to solve the problem upstream myself and have the small possibility that I either miss a newsletter and get spam anyway, or tip off some system that my email address is "real".