New subscribers: Any time a new subscriber joins your campaign.
Replies: If you have an autoresponder or broadcast set up to forward replies to you, those messages will go to notification addresses with this checked.
Bounces: If an email autoresponder or broadcast is returned as undeliverable due to an invalid email address, this setting will notify you.
Hang-ups: If someone calls in to your campaign, but hangs up does not leave a message, this setting will notify you.
Hot leads: Users who take an additional step to show interest. Currently only completing an event triggers the hot lead notification.
Attach audio: If someone leaves a message after calling in to your campaign, this setting will attach the message.
Subscriber updated: Notifies you when a subscriber's record is updated. Includes submitting a phone number on the Thank You page, edits using the edit link at the bottom of emails, and SMS responses that populate a subscriber field.