BuddyPress Activity Comment Notifier plugin emulates the facebook style notification for the comments made on user updates. It will show the notification to a user in following scenario
- When a user has an update and someone else comments on it
- When a user comments on someone's update and other users also comment on that update, all the users are notified
Does it sends an email notification?
No, It does not. It just shows the notification in the drop down when a user is logged in.