I checked the email I used for my Gravatar (the autogen image was cooler than the one that matches my OpenID), and I was surprised to find an automated Stack Overflow notifying me about a bounty I posted.
It told me I could opt out of these notifications, which I found odd because I wasn't aware I ever opted in to them. A study of my user profile shows a checkbox for "I'd like email notifications of activity on my questions and answers", which I have never toggled.
I find the on-site notification envelope to be far more useful, so I thought it less-than-optimal to use email notifications.
Why did I receive the email even with that setting turned off?