I hate that what's considered necessary transactional/'service update' is up to the service provider too though.

I use a pretty scammy credit score tracker thing in the UK, (it's not at all like it is in the US, not even a single 'it', but this service would love you to think 'it' is) just to keep an eye on for fraud really. But they recently decided that their monthly updates (don't tell you new score or if there's anything alarming or changed at all in the email obviously, click through to the website!) are a core component, a service update, and are therefore not required to feature an 'unsubscribe' link, nor to respect users' pre-existing 'unsubscribed' preference.

If a service doesn't provide an easy and obvious way to unsubscribe from unwanted emails—by my definition, not theirs—I personally have no qualms about marking them as spam and letting them take the reputation hit. The same applies if I never subscribed in the first place; I'm not going to click an "unsubscribe" link (which could well be malicious, and at the very least leaks the fact that I received the message) for a service I didn't sign up for in the first place and have no other connection with. If not subscribing didn't work then there is no reason to think that merely unsubscribing will prove any more efficacious.

It gets more complicated when the unwanted spam is from a service which I do want to receive notifications from (just not the junk mail). Most email clients offer rule-based classification which can help, but that is obviously a bit more work than just marking messages as spam.