php mx lookup and if then else - php

Question

I Try to made a - as I thinked - easy Script, which simply checks the MX Record of a Mail address and if it Matches, redirect to an specific URL.
Suddenly... I have no clue how to work it out. I found some things on google, but it seems not to work. Where is my Fault?
<title>Mailredirector</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<!-- ********** HEADER START ********** -->
<hr>
<br>
<!-- ********** HEADER ENDE ********** -->
<!-- ********** FORMULAR START ********** -->
<form method="post" action="mxnew.php">
<p style="text-align: center">
Bitte geben sie Ihre Mailadresse ein und klicken sie auf Senden<br>
<br>
<br>
<b>Email: </b><input type="email" name="email" id="email" style="height: 30px; width: 350px;"/>
<br>
<input type="submit" value="Check" id="dsubmit" name ="submit" style="width: 80px; height: 30px;"/>
</p>
</form>
<!-- ********** FORMULAR ENDE ********** -->
<!-- ********** FOOTER START ********** -->
<hr>
<!-- ********** FOOTER ENDE ********** -->
</body>
</html>
<?php
if (isset($_POST['submit'])) {
$email = $_POST['email'];
/* <----- Domain von Name trennen ----->*/
$domain = substr(strrchr($email, "#"), 1);
/* <----- MX Record und Domain prüfen ----->*/
function mxrecordValidate($email, $domain) {
$arr = dns_get_record($domain, DNS_MX);
if ($arr[0]['host'] == $domain && !empty($arr[0]['target'])) {
return $arr[0]['target'];
}
/* <----- Weiterleitungen an andere Domain ----->*/
if ($arr['target'] == mx.domain.com) {
Header ('location: http://google.ch');
die();
}
if ($arr['target'] == all01.mx.domain.ch) {
Header ('location: http://google.fr');
die();
}
else {
Header ('location: http://google.com');
die();
}
}
}
?>