The default functionality is for the Status to be set to Open whenever the customer replies via email.
This article explains how to update the status change when users are replying to tickets.
- Go to your Admin Panel > Tickets > Settings.
- Modify the Set tickets to this status on user reply option.
The default value for this setting is Open.
- Change it to
-- Do Not Change --so that the status persists on every ticket even for email responses.