1) User profile > Preferences
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2) Untick 'and receive email notifications of replies'.
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You can also untick 'automatically watch threads that you create or when you reply'. This means that if you add a post in a thread, you won't constantly get notifications whenever anybody adds anything to that thread. I find it's a pretty useful thing to untick
3) There are more alert settings in User profile > Alert Preferences, if you want to disable notifications for specific things.
Hope this helps!