class SomeCommand {
/**
 * config:
 *
 * swiftmailer:
 *   transport:  smtp
 *   encryption: ssl
 *   auth_mode:  login
 *   host:       smtp.example.com
 *   username:   your_username
 *   password:   your_password
*/
    public function execute(){
        $container = $this->getContainer();

        $mailer = $container->get('mailer'); // Swift_Mailer with smtp transport
        $queue = $container->get('mail-queue');

        while($mailMessage = $queue->get()){
            try{
                $mailer->send($mailMessage);
            } catch(\Exception $e){
                // some catch logic
            }
        }
    }
}