When you use the notify button, it first checks to see if there are any moderators specifically assigned to that forum. It also checks to see if any admins or global moderators have checked to receive these notifications in their "preferences" in the "my stuff" menu.
It then will send to all emails in that list that it found. If it didn't find anyone to notify, then it will send to the main forum email address.
So, if you're an admin, first thing to do is check under your Preferences and turn that on if you want to receive notifications.