The default functionality is for the Status to be set to Open whenever the customer replies via e-mail. In order to maintain the ticket status when a user responds, go to your Admin Panel > Tickets > Settings, and 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 e-mail responses.
How do I disable status change when users are replying to tickets?
or drag and drop files
Alina Maxi