Unchecking that box in your member profile page on both iFixit and Meta should take care of it.
We want to make this notifications more useful! We've been brainstorming a lot of ways of improving them internally, but I'm interested in hearing what all of you think.
Our initial thoughts are to have a new notification item in the menu so you can find out if you've got an accepted answer right away, rather than waiting for the nightly email. We're also talking about letting you choose the frequency of emails — so you could get a daily or weekly digest, for example.
What would make it easier to stay in touch with people's responses to your work? Let us know!