Log on to AA using a browser (not 1 of the mobile aps).
Click 'user cp' in the blue bar at the top of the page
Find 'edit options' in the left hand column.
Find "Default Thread Subscription Mode" in the options to the right.
Set the default to "no email notification"
If you want to clear email notifications of your currently subscribed threads:
Click 'user cp' again.
Find "list subscriptions" in the left hand column
Click the radio box at the top of the page to select all subscriptions
Scroll to the bottom right of the page and click the drop down menu and select "no email notification".