News forum posts are emailed out to members of that course area. It's possible to opt in and out of other forum discussions, depending how they are set up.
It is possible to stop ALL emails from forums being sent to your email address by making a change to your profile. TURNING THIS OFF COULD CAUSE YOU TO MISS IMPORTANT INFORMATION and college cannot be held responsible if you miss out on some communications if you have chosen to turn this off. This is a big step to take, so before you exclude yourself, go through the steps above.