Communicate with potential buyer through backend

Hello

I have set up a website with the car dealer theme.

When a car is listed and somebody posts a reaction or asks a question, the seller of the car gets a notification in his email-inbox. So far so good. When he or she logs in their account, they can read the message but then, when they want to reply to the person that asked the question, it isn’t the email address of that person that is in the “to” field …

Here I show the problem: https://www.youtube.com/watch?v=VzxmLy4j9AM

How can I fix this?

Thank you very much for the reply.