When you are signed in you need to go to the top right and click on settings
on the next screen you will see on the left hand side a couple of boxes the top one says "My Messages" the second one down says "Subscriptions" click on that and it should bring you to the next screen
on this screen you will see all the threads that you subscribe to on the right click all the boxes you want to change the notification on and then click the button under that labeled "Selected Threads" then change your option to Instantly, Daily, or Weekly.
If you wish you can set it up to always send you and email when you subscribe by going to settings, then on the right to general settings the set the option under "Default Thread Subscription Mode:"