> I hope they make it really strict. I'm sick of companies that send you spam ("newsletters") just because you interacted with them once, then when you unsubscribe, you get unsubscribed from that one list, so they keep spamming you just with a slightly different newsletter type.
Never interact with spam. Unsubscribing just tells spammers that your email address is actively being checked, and that you're the kind of person who clicks on links found in unsolicited messages. It can even end up getting you more spam (as you've noticed), and what looks like an innocent unsubscribe link can actually take you to a malicious website instead. You've really got nothing to gain by touching spam at all.
The best way to deal with the spam that makes it into your inbox, especially spam that comes from specific senders with predictable subject lines/body content like newsletters, is filtering. For example, just auto-delete anything from a domain you never want to hear from again. You never see it, and you leave them spending at least a little time/effort shouting uselessly into the void.
I tend not to auto-delete directly, but have things filtered into specific folders just in case. It takes almost no time to clear out when they get very full. Most filters are set once and forget.