I keep a pretty tidy inbox by studiously unsubscribing from advertorial mail as soon as I receive it. I make no exceptions. Consequentially, it's fairly easy to

I keep a pretty tidy inbox by studiously unsubscribing from advertorial mail as soon as I receive it. I make no exceptions. Consequentially, it's fairly easy to notice when an unsubscribe action didn't work. I've noticed a few times that a company I have unsubscribed from years ago will suddenly start sending me mail again. Usually I'll just re-unsubscribe and they'll go away again. I've also had it several times that I clicked on an Unsubscribe link and the resultant page indicated I had been removed from the list but I continued to receive mail noticeably past the date indicated ("it may take up to a week for your name to be removed, as some mail is queued in advance"). Conveniently, when I followed the link with my ad blocker disabled the request succeeded (without any change in appearance), but I actually stopped receiving their spam. I can't say anything about email newsletters, because I don't subscribe to them.