Using Delivered-To to deliver email and not the To in the mail header

Hi there,
i think this is a special problem. My ISP is receiving our emails.
When there are multiple names in the receiving list he set so many
emails.
Example : email to test@domain.com and new@domain.com in one email.
This comes to one email to Delivered-To : test@domain.com and
To :
test@domain.com, new@domain.com
the second email the same
Delivered-To : new@domain.com
To: test@domain.com, new@domain.com

thats O.K., but at our email-server whe fetch the mails from our ISP and
postfix will delivere the mail local. Now he looks at the To Field in the
mail header an put the mail twice. But if there are three receiptions and
more ....

So my question is, is it possible to say postfix to look only to the
Delivered-To Field or are there other tips ?

O. Matthaei