protected function applyMailTrapConfiguration($inboxId = null)
    {
        if (is_null($config = Config::get('services.mailtrap'))) {
            throw new Exception(
                'Set "secret" and "default_inbox" keys for "mailtrap" in "config/services.php."'
            );
        }

        $this->mailTrapInboxId = $inboxId ?: $config['default_inbox'];
        $this->mailTrapApiKey = $config['secret'];
    }