We have been receiving many messages and issue reports regarding emails flooded with notifications from groups and mass forwards. We have contacted Ning and they have provided some insight on how to manage this.
You can control your email settings by signing in, clicking Settings on the right hand side, then clicking the email tab (left side). There you can choose the kind of notifications you want to receive.
If you want to stop receiving email from comments, groups, events you have already followed, you will need to click the "Stop Following All" link on that page as well.
Please let us know if you are still experiencing trouble.
Elizabeth and Colleen