'admin@domain.com', 'administrator' => 'administrator@domain.com', 'root' => 'root@domain.com', ); if (isset($_POST['username']) && array_key_exists($_POST['username'], $users)) { $valid = false; } else if (isset($_POST['email'])) { $email = $_POST['email'][0]; foreach ($users as $k => $v) { if ($email == $v) { $valid = false; break; } } } echo json_encode(array( 'valid' => $valid, ));