mail à plusieurs destinataires ne marche pas

<td>avertir ?</td><td><input type="checkbox" name="envoi" value="oui"></td>

$envoi = $_post["envoi"];

	if ($envoi = 'oui') {
	
	$sql = "select * from matable where email <> null";
	$requete = mysql_query($sql) or die('erreur sql !<br>'.$sql.'<br>'.mysql_error());

	while( $result = mysql_fetch_array( $requete ) )
		{
		$destinataire = "email";
		$sujet = "mon sujet";
		$message = "mon message";
		mail($destinataire,$sujet,$message);
	}
	}
	else header("location: ../formulaire.php");

	if ($envoi = 'oui') {
	
	$sql = "select * from matable where email <> null";
	$requete = mysql_query($sql) or die('erreur sql !<br>'.$sql.'<br>'.mysql_error());

	while( $result = mysql_fetch_array( $requete ) )
		{
		$destinataire = 'email';
		$sujet = 'mon sujet';
		$message = 'mon message';
		$headers = 'from: monemail';
		mail($destinataire, $sujet, $message, $headers);
	}
	}
	else header("location: ../formulaire.php");

$destinataire = 'email';

$email = $result['email'];

$destinataire = $email;

$email = $result['email'];

	$sql = "select * from matable where email <> null";

	$sql = "select email from matable where email <> null";

		$destinataire = $result['email'];
		$sujet = 'mon sujet';
		$message = 'mon message';
		$headers = 'from: moi@xyz.com';
		mail($destinataire, $sujet, $message, $headers);

if ($envoi == 'oui')

if ($envoi = 'oui')