empty x-envelope at bounce

Hi,
i use postfix with smtp-relay. problem is, if i send an email with a non
existing recipient, postfix (or the relay-server?) deletes the
X-Envelope-From field. postfix then tries to inform the sender of the
email via the relay-server which deny that email ('550 no valid sender
in Sender:, Reply-To:, or From:').

my question, is it possible to configure postfix to generate a valid
X-Envelope-From field ?

Christian