Found a mailing list ("marketing") service that allowed you to sign up with a +, but any 'unsubscribe' was a link to a URL with your email in it, with the + sign in it, and... the unsubscribe page could magically never find your address to unsubscribe you. I submitted this as a bug report to the service, and was brushed aside. At that time, I also had a couple friends who worked there, and tried to run it up the flagpole there, and I was told about half the folks there didn't understand the problem, and the other half didn't really care, because the + trick was seen as very niche. So I started reporting all the newsletters I got as 'spam' - well after I'd tried to unsubscribe.