Form mail

har hentet den form mail men hvor for virker den ikke:

<html>

<head>
<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
<meta name="ProgId" content="FrontPage.Editor.Document">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Formmail</title>
</head>

<body>

<b><font face="Verdana" size="1">Kontakt mig:</font></b><br>



<?php
if(isset($_POST['navn'])){
    mail("din@email.dk", "$_POST[emne]", "Beskeden er:\n $_POST[besked]", "From: $_POST[navn] <$_POST[mail]>");
    echo "<b> Din mail er nu sendt </b>";
}
?>

</font>

<form action="<?php echo $SERVER['PHP_SELF']; ?>" method="post">
<b><font size="1"><font face="Verdana">Navn:</font><br>

</font></b>
<font size="1">
<input type="text" name="navn" size="15" style="font-family: Verdana; font-size: 8pt; color: #000000; border: 1px solid #000000; background-color: #D1D7DC"><br>

</font><b><font size="1"><font face="Verdana">Email:</font><br>

</font></b>
<font size="1">
<input type="text" name="mail" size="15" style="color: #000000; font-family: Verdana; font-size: 8pt; border: 1px solid #000000; background-color: #D1D7DC"><br>

<font face="Verdana">

<b>Emne:</b></font></font><b><font size="1"><br>

</font>
</b>
<font size="1">
<input type="text" name="emne" size="15" style="color: #000000; font-family: Verdana; font-size: 8pt; border: 1px solid #000000; background-color: #D1D7DC"><br>

<font face="Verdana">

<b>Besked:</b></font></font><b><font size="1"><br>

</font>
</b>
<font size="1">
<textarea name="besked" rows="6" cols="30" size="20" style="color: #000000; font-family: Verdana; font-size: 8pt; border: 1px solid #000000; background-color: #D1D7DC"></textarea><br>
<br>
<input type="submit" value="Send" style="color: #000000; font-family: Verdana; font-size: 8pt; border: 1px solid #000000; background-color: #D1D7DC">
</form>

</font>

</body>

</html>