email spoof

<form action="spoofer.php" method="GET">
<p>To Email: <input type="text" name="email" /></p>
<p>Subject: <input type="text" name="header" /></p>
<p>From Email: <input type="text" name="fake" /></p>
<p>Email Message: <textarea name="message"></textarea></p>
<p><input type="submit" value="Send Email"></p>
</form>

-----------------------------/----------///////------

<?php
 if (!isset($_GET[email]) || empty($_GET[email]))
 {
 echo "TO field is empty";
 exit;
 }
 else
 {
 $to = $_GET[email];
 }
 if (!isset($_GET[header]) || empty($_GET[header]))
 {
 echo "Subject is missing";
 exit;
 }
 else
 {
 $subject = $_GET[header];
 }
 if (!isset($_GET[fake]) || empty($_GET[fake]))
 {
 echo "FROM email address is missing";
 exit;
 }
 else
 {
 $fake = $_GET[fake];
 }
 if (!isset($_GET[message]) || empty($_GET[message]))
 {
 echo "email message box is empty";
 exit;
 }
 else
 {
 $message = $_GET[message];
 }
 $headers = "MIME-Version: 1.0" . "\r\n";
 $headers .= "Content-type:text/html;charset=iso-8859-1" . "\r\n";
 $headers .= "From: " . $fake . " <" . $fake . ">" . "\r\n";
 if (mail($to, $subject, $message, $headers))
 {
 echo"<h1>Success</h1>\n";
 echo"<p>The e-mail was successfully sent to <i>" . $to . "</i></p>\n";
 echo"<p>From: <i>" . $fake . "</i></p>\n";
 echo"<p>Subject: <i>" . $subject . "</i></p>\n";
 echo"<p>Message:</p>\n";
 echo"<p><b>" . $message . "</b></p>";
 }
 else
 {
 echo"<h1>Error!</h1>\n";
 echo"<p>The mail() function failed.</p>";
 }
 ?>