yes, you can easily do this (i know, those emails get out of hand fast, don't they !). go to your
user control panel (link in the blue nav bar at the top of the page). in the menu on the left, select "edit options". there you can modify the default thread subscription mode. in the user cp, you can also see your subscribed threads, and using the dropdown menu at the end of the list modify your subscription choice.
enjoy the forum !