This plugin allow group members to receive email updates about new forum topics, forum posts and group activity updates. In order to get updates, a user must either subscribe or super-subscribe to the group. Subscribed users will get all new forum topics, but not the subsequent comments (same with activity posts). If a user super-subscribes to the group, they will get an email will all new content.
By default, the plugin will send email updates to a user for any comments on a forum topic they create or comment on.
This plugin is in early beta status and not yet suitable for using on production websites.
Plugin Homepage: http://namoo.co.uk/