protected function buildTransportConfig()
    {
        switch ($this->transport) {
            case Module::TRANSPORT_SMTP: {
                return [
                    'class' => 'Swift_SmtpTransport',
                    'host' => $this->smtpHost,
                    'username' => $this->smtpUsername,
                    'password' => $this->smtpPassword,
                    'port' => $this->smtpPort,
                    'encryption' => $this->smtpEncryption,
                ];
            }
            default:
                return [
                    'class' => 'Swift_MailTransport',
                ];
        }
    }