Backend\Modules\Mailmotor\Form\SettingsType::getPossibleMailEngines PHP Method

    private function getPossibleMailEngines()
    {
        // init dropdown values
        $ddmValuesForMailEngines = array();
        // Add empty one
        $ddmValuesForMailEngines['not_implemented'] = ucfirst(Language::lbl('None'));
        // loop all container services to find "mail-engine" gateway services
        foreach ($this->serviceIds as $serviceId) {
            // the pattern to find mail engines
            $pattern = '/^mailmotor.(?P<mailengine>\\w+).subscriber.gateway/';
            $matches = array();
            // we found a mail-engine gateway service
            if (preg_match($pattern, $serviceId, $matches)) {
                // we skip the fallback gateway
                if ($matches['mailengine'] == 'not_implemented') {
                    continue;
                }
                // add mailengine to dropdown values
                $ddmValuesForMailEngines[$matches['mailengine']] = ucfirst($matches['mailengine']);
            }
        }
        return $ddmValuesForMailEngines;
    }