How do i stop DFN backscater

Hi 
One of my clients made a setup that all her mails are forwarded to remote
ISP
Unfortunatly i noticed that sometimes i get 450 error from destination ISP
this triggers Delivery Failure Notice wich is naturally sent to this ISP
Is there a way to stop this endless loop ?
Im using postfix 2.5.8 
Im tryin to setup a prce filter that compares To: field with message body
where is the info about Delayed mail to [EMAIL PROTECTED] and try to siscard 
mail
if the email from body maches the email from To field but somehow i cant
figure the right regexp
Any help would be appreciated.