not able to send arabic email with good caracters

i want to send an arabic email with using php , but it gives me others caracters , how to send it with the arabic caracters ? this is my code :

$subject = $_POST['subject'];
$message = $_POST['message'] . "nn" . 'Regards, ' . $_POST['name'] . '.';
$headers = 'From: ' . $_POST['name'] . "rn" . 'Reply-To: ' . $_POST['email'] . "rn" . 'X-Mailer: PHP/' . phpversion();

mail($to, $subject, $message, $headers);

if( $_POST['copy'] == 'on' )
{
    mail($_POST['email'], $subject, $message, $headers);
}
}
?>