thanks for the reply.

What I don't understand is: The email server is a closed relay. Only authenticated users are allowed to send emails.

So the sent emails have an existing email address (although faked) and are sent through a email server somewhere in the world.

If those emails get rejected, why is the NDR being sent to me (the existing email address) ? And why can't Xeams recognize this and treat it as Spam ?

Thanks again