How can I be notified when user response to the message in SR?

Summary:

When composing a response from SR--> Messages, user receives email notification. How can I be notified when user replies to the email? The user reply can be seen in Messages (as shown in below snapshot) but every time I have to check it manually whether user responded or not. Tried to achieve this through a trigger with MessageTypeCD == 'ORA_SVC_RESPONSE' but this event triggers only when I compose a message from SR messages. Whereas when user reply to the email notification, the event doesn't trigger.

Note: In our scenario, user will not response through 'Customer Entry'. User should response the email which is received via Messages-> Response.