How to receive an email notification every time a discussion is added or modified for an artifact ?
Click your avatar in the upper right corner of Rally, select the Notification Rules tab.
Click + Add New, Enter a descriptive Name, select your Work Product Type from the drop-down. In the Condition section, select the Discussions field and select "Changed" operator.
This means that every time the Discussions field will change, which a new discussion is added, or a discussion is amended then the notification rule will fire and the email will be sent. Click Save.