At the top of the page, just under the ads, is a line of options. Click the next to last on right - Profile.
On the left, under Control panel, is a list of options.
Click on the fourth down - Edit Options
On the right are a number of orange framed areas
Go to the second - Messaging and notification
It contains some blue framed areas
Go to the second - Default thread subscription mode
Set the window to No e-mail notification
MOST IMPORTANT -
Scroll all the way to the bottom and click Save changes