How can you change the status of a case based on who updates the case ?

If a client responds to a ticket in an email and the case thread gets updated how can you change the status so you know ? I tried programming a workflow but can not seem to make anything work.

Version 7.9.7
Thank You !

can you show the workflow you put together?

To be honest I am not sure how to set that up, I can not tell what field was updated, and if the user or the contact updated the case. Also I tried to get the AOP Case Status Change to work and no matter what I put in there it does not change.