Oops...batch edit mistake. D'oh!!!
Using Jamroom
On my Ning site, which is still operating, I have deleted comment walls for most groups because people tend to use comments to attempt communicating with members of the group, not realising that there is no notification of comments to group members through email.
In a Ning group, when anyone posts a message in the group forum, all members of the group are notified about the new message, through email. They don't have to actively log in to monitor the group activity. Unless they turn off that particular messaging option in their privacy settings.