Envoi MDP par mail: problème hash MD5

<form name="form1" method="post" action="sendpass.php">
<input onclick="this.value='';" value="Votre e-mail" name="email_to" id="mail_to" size="25" /> 
<input name="Submit" value="Envoyer" type="submit" />
</form>

<?php //début code php

$host="localhost"; // Host name 
$username="xxxxx"; // Mysql username 
$password="xxxxxxx"; // Mysql password 
$db_name="xxxxx"; // Database name 


//Connect to server and select databse.
mysql_connect("$host", "$username", "$password")or die("cannot connect to server"); 
mysql_select_db("$db_name")or die("cannot select DB");

if (isset($_POST['Envoyer'])){

$email_to=$_POST['email_to'];

function mdpAleatoire($longueur=5)
{
$mdp = '';
// liste des caractères pour créer le mot de passe
$caracteres = 'NBVCXWQSDFGHJKLMPOIUYTREZA1234567890';
// longueur de la chaine
$nombre_caractreres = strlen($caracteres);
// On initialise la fonction aléatoire
srand(microtime()*1000000);
// On boucle sur le nombre de caractères voulus
for($i = 0; $i < $longueur; $i++)
{
// tirage d'un nombre inférieur ou égal à la longueur de la chaine de caractères
$position = rand(0, $nombre_caractreres-1);
// on cumule le caractère dans le mot de passe
$mdp = $mdp.substr($caracteres, $position, 1);
}
// on renvoie le mot de passe (on peut le stocker quelque part...)
return $mdp;
}
$newpass = mdpAleatoire();
$newpasshash = md5($newpass);

$query = new MysqlQuery($conn);
$qresult = $query->GetSingleQuery('--SINGLE',"SELECT user_password FROM _users WHERE user_email = '{$email_to}';",array("user_password"));


if($qresult < 0)
{
// Error
header("Location: edit_information.php?e=2");
exit;
}


// Store information in database
$qresult = $query->SendSingleQuery("UPDATE _users SET user_password = '{$newpasshash}' WHERE user_email = '{$email_to}';");

if($qresult == -1)
{
// Error occurred
header("Location: edit_information.php?e=2");
exit;
}
else
{
// Success, added 
header("Location: edit_information.php?e=P");
exit;
}

}

$to=$email_to; 

// Your subject 
$subject="Your password here"; 

// From 
$header="from: your name <admin@xxxxx.net>"; 

// Your message 
$messages= "Your password for login to our website \r\n";
$messages.="Your password is $newpass \r\n";
$messages.="more message... \r\n";

// send email 
$sentmail = mail($to,$subject,$messages,$header); 


// if your email succesfully sent 
if($sentmail){
echo "Your Password Has Been Sent To Your Email Address.";
}

?>