There are two email notification systems: one for replies and one for new posts.
When you check the box when composing a post, you will get 'reply' notifications.
If you use the "Email Notifications" link in the upper right hand corner, you are subscribing to the mailing list for the forum to receive notifications of NEW posts.
Those are two different systems.
At this time, you can not turn off the 'reply' notifications if you have checked the box. Nor can you update the email address on that part. (you can on the New post notifications). (I know, it's imperfect)