How can I send the mail once?

I am working on a marketplace plugin. If the vendors do not accept the order within the date range I set, the order will be cancelled. For this, I have determined a time period of order date +3 days. So far, so good.

How Can I Change Default Reply ToEmail

I want to set the SMTP settings manually instead of using a plugin. I did this using this resource. However, there is a problem.
If the user clicks “Reply”, a different e-mail appears. Probably I’ve described this before with the plugin. However, I cannot remove it. If I make a new definition as below, it creates a new reply e-mail. Therefore, the past is not erased.
What I want: If the user clicks to reply to the incoming e-mail, only smtp_from e-mail should appear.