note 18584 deleted from function.mail by jimw

Adding a 'Reply-To:' header doesn't cut it, since this is typically something only your MUA is interested in. Great for actual replies, but useless if the message bounces. Error messages get sent to the sender of the message, according to the SMTP-envelope (also called: Return-path). Usually, with mail sent from PHP, this is nobody@localhost.localdomain (depending on your setup, of course). The only way to change the envelope-sender, is by putting "-f<address>" in the 5th parameter. Adding a "Return-path:" header yourself is not the way to go, since that's not the way it's intended to work and it probably won't (see RFC 2821, section 4.4). One thing you _can_ try however, is adding an "Errors-to:" header to your message. But again, not all MTAs support this, so it may not work.