I'm not a Community Server expert, but it appears that there are two situations which will trigger emails. Both of them require this option be set to 'Yes' under the Email Tab in your profile:
"Enable Email Notifications of forum/thread subscriptions and replies to my posts."
1) You click 'Enable Email Subscription' on a thread. This you can stop by clicking 'Disable Email Subscription' on that thread.
2) Someone posts a Reply to one of your Posts. This cannot be stopped unless both features are disabled by setting the option in your profile to 'No.'
David Neal Parsons
www.entityspaces.net