Right now, whenever someone posts to a discussion, either as a reply or a post, they are automatically subscribed to that Discussion. I can understand that this might allow for seeing any replies to the post, but it also results in seeing everyone else's posts and can quickly fill up someone's email. I believe other programs will automatically only post any replies to the specific user's post and not subscribe the person to the entire discussion unless the user specifically subscribes to the Discussion.
There could be a default set in the main settings that would cover this - something like:
"When posting to a Discussion"
- Automatically subscribe to that Discussion
- Only email responses to own posts
- Allow users to subscribe to Discussion