[otrs] Question about sorting

Hi, I have a question about sorting tickets. In the new messages folder, we want to be able to sort the tickets there according to whether ther have been any responses. Our current sorting is apparently according to creation date, with newest at the top. But if a "customer" responds to a ticket, then the ticket remains at the same place in the list and I would like it to pop up to the top. Any ideas? Jeremy Cook