Variable global ?

Réponse acceptée !
Essaye :

if (isSet($_POST['submit']))
{
    $id = $_POST['id'];

    foreach ($id as $cle => $val)
    {
        echo $val.'<br />';
    }
}

En ayant comme formulaire :

<form action="mapagedereception.php" method="post">
.....liste des champs....
<input type="checkbox" name="id[]" value="1" />1<br />
<input type="checkbox" name="id[]" value="2" />2<br />
<input type="checkbox" name="id[]" value="3" />3<br />
<input type="hidden" name="submit" />
<input type="submit" value="Valider" />
</form>