Io intendevo propio cambiare il testo, ad esempio:
This is the Postfix program at host xxxxx.yyy.it.

I'm sorry to have to inform you that your message could not be
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to <postmaster>

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The Postfix program
Volevo ad esempio togliere il fatto che si trattasse di Postfix, ed al limite metterlo, oltre che in inglese, anche in altre lingue!