Click on User CP.
From the left hand menus select Edit Options.
Scroll down to second option, Messaging & Notifications.
Find: Default Thread Subscription Mode.
From pull down menu, select "No email notifications".
You will also need to check mark all of your subscribed threads and change to no email (select from drop down menu at bottom of page) also, or your previously subscribed threads will continue to send emails.
If you get stuck, send me a PM and I'll walk you through it.
If you can't see the bright side of life, polish the dull side.