'admin@domain.com', 'administrator' => 'administrator@domain.com', 'root' => 'root@domain.com', ); if (isset($_POST['username']) && array_key_exists($_POST['username'], $users)) { $valid = false; $message = 'The username is not available'; } else if (isset($_POST['email'])) { $email = $_POST['email']; foreach ($users as $k => $v) { if ($email == $v) { $valid = false; $message = 'The email is not available'; break; } } } echo json_encode( $valid ? array('valid' => $valid) : array('valid' => $valid, 'message' => $message) );