Send a message when a comment is left
How about the modules - 

Comment Notify


  Comment Notify is a lightweight tool to send notification e-mails to visitors about new, published comments on pages where they have commented. Comment Notify works for both registered and anonymous users.


or

Notify


  The notify module allows users to subscribe to periodic emails which include all new or revised content and/or comments of specific content types, much like the daily newsletters sent by some websites.


and see Email notification for new comments