UNIX for Advanced & Expert Users

I wanted to copy (not forward but copy) all incoming email to another address of mine. It worked, but now I encountered an infinite loop problem: When the second address doesn't like the content and bounces the message back, the bounce message will be sent back and forth.

So, what I have in .procmailrc was:

:0c:
* .
! new@address.com

How do I change that so that in case the sender contains "Mail Delivery Subsystem" or "MAILER-DAEMON", the message will not be copied at all?

From procmailex:

Suppose you have two accounts, you use both accounts regularly, but they are in very distinct places (i.e., you can only
read mail that arrived at either one of the accounts). You would like to forward mail arriving at account one to
account two, and the other way around. The first thing that comes to mind is using .forward files at both sites; this
won\u2019t work of course, since you will be creating a mail loop. This mail loop can be avoided by inserting the following
recipe in front of all other recipes in the $HOME/.procmailrc files on both sites. If you make sure that you add the
same X-Loop: field at both sites, mail can now safely be forwarded to the other account from either of them.

Code:

              :0 c
              * !^X-Loop: yourname@your.main.mail.address
              | formail -A "X-Loop: yourname@your.main.mail.address" | \
                 $SENDMAIL -oi yourname@the.other.account