My websites sends mails to my users, and so far, my address is used as from, even if I didn't send that mail. I would like to change this to a noreply@... address, but since the users reply quite often to these emails, I would like to send them a helpful reject message. Mails to other non existing addresses should be unchanged.
How can I do so? I'm using Postfix 2.7.0 on Ubuntu 10.4.