Probleme mail() Lotus Notes

j'ai un petit probleme quand j'utilise la fonction mail(); de php pour envoyer un message a un lotus notes il ne prend pas en charg les é à .... et pour tant jai bien fais une fonction qui converti les caractere spéciaux avec str_replace(); pouvez vous m'aidez je vous serait bien reconnaissant merci en avance

Voici mon code:

<?

//probleme
$probleme=$_POST ['probleme1'];
$user=$_POST ['user2'];
// pas d'email pour sécurité merci
$to="*********";
$sujet="probleme";
$lettre="$user\n\n$probleme";

switch ("rien") {

case ($probleme==null):
echo " Écrivez votre probleme";

echo "<br>";
echo " Vous pouvez fermer cette page";
break;

case ($probleme!==null):

$user=str_replace("é","é", $user);
$user=str_replace("Ã&#168;","è", $user);
$user = str_replace("ê","ê", $user);
$user = str_replace("ë","ë", $user);
$user = str_replace("î","î", $user);
$user = str_replace("ï","ï", $user);
$user = str_replace("Ã","à", $user);
$user = str_replace("à&#164;","ä", $user);
$user = str_replace("à¢","â", $user);
$user = str_replace("à&#8218;","Â", $user);
$user = str_replace("à´;","ô", $user);
$user = str_replace("à¶","ö", $user);
$user = str_replace("à»","û", $user);
$user = str_replace("à¹","ù", $user);
$user = str_replace("à&#188;","ü", $user);
$user = str_replace("à§","ç", $user);

$probleme=str_replace("é","é", $probleme);
$probleme=str_replace("Ã&#168;","è", $probleme);
$probleme = str_replace("ê","ê", $probleme);
$probleme = str_replace("ë","ë", $probleme);
$probleme = str_replace("î","î", $probleme);
$probleme = str_replace("ï","ï", $probleme);
$probleme = str_replace("Ã","à", $probleme);
$probleme = str_replace("à&#164;","ä", $probleme);
$probleme = str_replace("à¢","â", $probleme);
$probleme = str_replace("à&#8218;","Â", $probleme);
$probleme = str_replace("à´;","ô", $probleme);
$probleme = str_replace("à¶","ö", $probleme);
$probleme = str_replace("à»","û", $probleme);
$probleme = str_replace("à¹","ù", $probleme);
$probleme = str_replace("à&#188;","ü", $probleme);
$probleme = str_replace("à§","ç", $probleme);

mail ($to,$sujet,$lettre);
echo " Votre message a bien été envoyé";
echo "<br>";
echo " Vous pouvez fermer cette page";
break;
}
?>