My god I hate email notifications. But that's more because I'm one of those guys who posts everywhere, rather than just where they really are interested ;D
I looked through settings and I couldn't find anything.
However, if you look at the bottom of a thread where all the buttons are like 'Reply' there is a 'Notification' button as well, and if you click it you will have email notifications for that thread. So you just have to remember to click it for the threads you want to be notified on