Verify[Help]

<?PHP
include('config.php');
/*
Forgot Password script
*/
if ($_POST['Submit']) //Proceed if the submit button was pressed.
{
$Username = htmlspecialchars($_POST['username']); //Variable that contains the posted username.
$user=mysql_query("SELECT * FROM `verification` WHERE `username` = '$Username'");
$email = "SELECT `email` FROM `members` WHERE `username` = '$Username'";
$code = "SELECT `code` FROM `verification` WHERE `username` = '$Username'";
//counts the number of rows
$user = mysql_num_rows($user);
if (empty($Username)) //If the username field was left empty exit the script(with reason).
{
die("Insert Username");
}
if ($user == 0) 
{
die("Already Done!");
}
$link = "https://$host$self?verify&code=$code";
mail($destinatari, $oggetto, $messaggio, $intestazioni);
//message sent now lets tell them to check there email
echo "Sent";
} else {
//Display the form(HTML)
?>