php/html script verstuurd geen email. (contact formulier)

<form name="contactform" method="post" action="send_form_email.php">
<table width="450px">
<tr>
<td valign="top">
<label for="voornaam">voornaam *</label>
</td>
<td valign="top">
<input type="text" name="voornaam" maxlength="50" size="30">
</td>
</tr>
<tr>
<td valign="top"">
<label for="achternaam">achternaam *</label>
</td>
<td valign="top">
<input type="text" name="achternaam" maxlength="50" size="30">
</td>
</tr>
<tr>
<td valign="top">
<label for="EmailAdres">Email-Adres *</label>
</td>
<td valign="top">
<input type="text" name="EmailAdres" maxlength="80" size="30">
</td>
</tr>
<tr>
<td valign="top">
<label for="telefoonnummer">telefoonnummer</label>
</td>
<td valign="top">
<input type="text" name="telefoonnummer" maxlength="30" size="30">
</td>
</tr>
<tr>
<td valign="top">
<label for="postcode">postcode</label>
</td>
<td valign="top">
<textarea name="postcode" maxlength="6" cols="25" rows="6"></textarea>
</td>
</tr>
<tr>
<tr>
<td valign="top">
<label for="straat">straat + nummer</label>
</td>
<td valign="top">
<textarea name="straat" maxlength="1000" cols="25" rows="6"></textarea>
</td>
</tr>
<tr>
<tr>
<td valign="top">
<label for="probleem">probleem</label>
</td>
<td valign="top">
<textarea name="probleem" maxlength="1000" cols="25" rows="6"></textarea>
</td>
</tr>
<tr>
<I>Op welke dagen kunnen we contact met u opnemen:</I><BR>
<BR>
<SELECT NAME="keuzen">
<OPTION>Maandag</OPTION>
<OPTION>Dinsdag</OPTION>
<OPTION>Woensdag</OPTION>
<OPTION>Donderdag</OPTION>
<OPTION>Vrijdag</OPTION>
<OPTION>Zaterdag</OPTION>
<OPTION>Zondag</OPTION>
<OPTION>alleen werkdagen</OPTION>
</SELECT>
<td colspan="2" style="text-align:center">
<input type="submit" value="Submit">
</td>
</tr>
</table>
</form>

<?php
if(isset($_POST['email'])) {

// EDIT THE 2 LINES BELOW AS REQUIRED
$email_to = "[email protected]";
$email_subject = "contact formulier";


function died($error) {
// your error code can go here
echo "We are very sorry, but there were error(s) found with the form you submitted. ";
echo "These errors appear below.<br /><br />";
echo $error."<br /><br />";
echo "Please go back and fix these errors.<br /><br />";
die();
}

// validation expected data exists
if(!isset($_POST['voornaam']) ||
!isset($_POST['achternaam']) ||
!isset($_POST['EmailAdres']) ||
!isset($_POST['telefoonnummer']) ||
!isset($_POST['Postcode']) ||
!isset($_POST['Straat']) ||
!isset($_POST['Probleem']) ||
!isset($_POST['Keuzen'])) {
died('We are sorry, but there appears to be a problem with the form you submitted.');
}

$voornaam = $_POST['voornaam']; // required
$achternaam = $_POST['achternaam']; // required
$EmailAdres = $_POST['EmailAdres']; // required
$telefoonnummer = $_POST['telefoonnummer']; // required
$Postcode = $_POST['Postcode']; // required
$Straat = $_POST['Straat']; // required
$Probleem = $_POST['Probleem']; // required
$Keuzen = $_POST['Keuzen']; // required

$error_message = "";
$email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}$/';
if(!preg_match($email_exp,$email_from)) {
$error_message .= 'The Email Address you entered does not appear to be valid.<br />';
}
$string_exp = "/^[A-Za-z .'-]+$/";
if(!preg_match($string_exp,$voornaam)) {
$error_message .= 'The First Name you entered does not appear to be valid.<br />';
}
if(!preg_match($string_exp,$achternaam)) {
$error_message .= 'The Last Name you entered does not appear to be valid.<br />';
}
if(strlen($comments) < 2) {
$error_message .= 'The Comments you entered do not appear to be valid.<br />';
}
if(strlen($error_message) > 0) {
died($error_message);
}
$email_message = "Form details below.\n\n";

function clean_string($string) {
$bad = array("content-type","bcc:","to:","cc:","href");
return str_replace($bad,"",$string);
}

$email_message .= "voornaam: ".clean_string($voornaam)."\n";
$email_message .= "achternaam: ".clean_string($achternaam)."\n";
$email_message .= "email-adres ".clean_string($EmailAdres)."\n";
$email_message .= "telefoonnummer: ".clean_string($telefoonnummer)."\n";
$email_message .= "Postcode: ".clean_string($postcode)."\n";
$email_message .= "Straat: ".clean_string($straat)."\n";
$email_message .= "Probleem: ".clean_string($probleem)."\n";
$email_message .= "contactdag.: ".clean_string($Keuzen)."\n";

// create email headers
$headers = 'From: '.$email_from."\r\n".
'Reply-To: '.$email_from."\r\n" .
'X-Mailer: PHP/' . phpversion();
@mail($email_to, $email_subject, $email_message, $headers);
?>

<!-- html -->

hoi

<?php
}
?>