Is this the functionality you are referencing here? These arrows were present in version 14 and allowed you to navigate between replies:
The latest release of SmarterTrack received a visual update and it looks like this functionality was removed in the process. I can definitely see use in bringing it back so I'm going to submit a feature request on this for you now.
Kyle Kerst
IT Coordinator
SmarterTools Inc.
www.smartertools.com