Email in php/html is showing all the user's email , how do i add CC so the user can't see other user's email

i can send email but all the user kan se all the email i try to add cc but it is not vorking so nav i hope that you smart user kan help me with my problem $to = $_POST['email'];$from = "bladnyt@dhl-hund.dk";$subject = $_POST['sub'];$message = $_POST['msg'];$headers = "From: $from";

// boundary 
$semi_rand = md5(time());
$mime_boundary = "==Multipart_Boundary_x{$semi_rand}x";

// headers for attachment 
$headers .= "\nMIME-Version: 1.0\n" . "Content-Type: multipart/mixed;\n" . " boundary=\"{$mime_boundary}\"";

// multipart boundary 
$message = "This is a multi-part message in MIME format.\n\n" . "--{$mime_boundary}\n" . "Content-Type: text/plain; charset=\"iso-8859-1\"\n" . "Content-Transfer-Encoding: 7bit\n\n" . $message . "\n\n";
$message .= "--{$mime_boundary}\n";

// preparing attachments
for ($x = 0; $x < count($files); $x++) {
    $file = fopen($files[$x]['tmp_name'], "rb");
    $data = fread($file, filesize($files[$x]['tmp_name']));
    fclose($file);
    $data = chunk_split(base64_encode($data));
    $name = $files[$x]['name'];
    $message .= "Content-Type: {\"application/octet-stream\"};\n" . " name=\"$name\"\n" .
            "Content-Disposition: attachment;\n" . " filename=\"$name\"\n" .
            "Content-Transfer-Encoding: base64\n\n" . $data . "\n\n";
    $message .= "--{$mime_boundary}\n";
}
// send

$ok = mail($to, $subject, $message, $headers);
if ($ok) {
    echo "<p>mail sent to $to!</p>";
} else {
    echo "<p>mail could not be sent!</p>";
}

}