bad email addresses not returning mail

I have been having this problem for a couple of years now and can't find anyone who can explain this.

I run php on my sites which are all on shared hosting.
I use the following code to generate email headers.
The problem is that I cannot get any "undeliverable emails" back.
Any ideas?
Linda

<?php
$from = "webmaster@LakeHillsFairfield.com";
$header = "MIME-Version: 1.0\r\n";
$header .= "Content-type: text/html; charset=iso-8859-1\r\n";
$header .= "From: Lake Hills <$from>\r\n";
$header .= "Reply-to: Lake Hills <$from>\r\n";

$header .= "Errors-to: Lake Hills <lkrlinda@aol.com>\r\n";

$header .= "X-Sender: < $from >\n";
$header .= "X-Mailer: lakehillsfairfield.com form\n"; // mailer
$header .= "X-Priority: 1\n"; // Urgent message!
$header .= "Return-Path: <webmaster@lakehillsfairfield.com>n";

$ENV{'QMAILHOST'} = "lakehillsfairfield.com";

$ENV{'MAILHOST'} = "lakehillsfairfield.com";

$ENV{'QMAILUSER'} = "lkrlinda@optonline.net";

$recipient = "junkemail@junkmail.com";

mail($recipient, "test", "test", $header);

?>

Try this:

* F A N T A S T I C * !!!!!
CAn't believe it!
It has had many people stumped for a long time!
I presume the -f means the delivery failure email address?
THANK YOU SO MUCH!

Yeah, I think that's what the -f means. An administrator of one of the hosts I work with told me about this option because he got tired of getting bounced mail from my forums.