So I was receiving emails from a club that wanted me to put myself on their guest lists for events. I kept trying to unsubscribe, but the link for it never worked. In a fit of angry proactiveness, I sent them a threat email citing the Cal. Business Code damages on spammers who do not provide an opt-out feature (described here).
A few days later, of course I got another email from them, telling me about some event. But then, I clicked unsubscribe, and it worked.