Bounce email

Bounce email

While setting up CNAME we have to create a host name (example form.domain.com)

Actually we don't have any address email like that
bounce@form.domain.com

Furthermore
sender adresss noreply@domain.com is a virtual address, just to send the notification.

In both case report says that users are not found, and it's right because both email addresses don't exist.

How can I solve it?

Thanks