You have confused anonymous users with staged users.
If the reply email has been sent and has been bounced it is possible that you will find the error in Emails> Bounced > Email type column
By clicking on the email type error you may see the response from the email provider (generally near the end of the Subject Body:
For example
<my-address@example.com>: Host or domain name not found. Name service error for
name=example.com type=AAAA: Host not found
This can help you figure out where the problem is.