LOL what a pain in the BUTT! I went through the same thing FOREVER! I know it is annoying as ALL get out! .....
I can get you close------>
Go to "USER CP" in the upper left corner...the first button in the blue bar. Then scroll down to "EDIT OPTIONS" on the left. It is on that page I believe. You will have to look for the box to check.
You experience will be much nicer! Enjoy!
EDIT: I think you will still get e-mails on the threads you are already subscribed to though. When you think you have it, start another thread and ask for someone to reply and see if it stopped. As far the threads that you are "Grand Fathered in", I don't know. Maybe someone else can help.