$user_email=@$_POST['user_email'];
$user_name=@$_POST['user_email'];
if ($user_email){

$exists=false;
global $wpdb;
$users = $wpdb->get_results("SELECT * FROM `WP_MAILLIST`;");
foreach ($users as $user) {
# check users table against new user
if ($user->user_email==$user_email) {
$exists=true;
}
}//end foreach
if ($exists==false){
# add if not there
$num = rand(100000, 999999);
$result=$wpdb->query("INSERT INTO WP_MAILLIST (mail_key, user_name, user_email, user_registered, listed) VALUES ('$num', '$user_name', '$user_email', 'false', 'true')");
}

}
?>