email is not going to treehouse local mail

     <?php

      require __DIR__ . '/vendor/autoload.php';
      date_default_timezone_set('Asia/Calcutta');

      $app = new \Slim\Slim( array(
      'view' => new \Slim\Views\Twig()
       ));

      $view = $app->view();
      $view->parserOptions = array(
      'debug' => true
      );

      $view->parserExtensions = array(
          new \Slim\Views\TwigExtension(),
      );

     $app->get('/', function() use($app){
          $app->render('about.twig');
      })->name('home');

     $app->get('/contact', function() use($app){
         $app->render('contact.twig');
      })->name('contact');

      $app->post('/contact',function() use ($app){
      $name = $app->request->post('name');
      $email = $app->request->post('email');
      $msg = $app->request->post('msg');

       if(!empty($name) && !empty($email) && !empty($message)){
        $cleanName = filter_var($name, FILTER_SANITIZE_STRING);
        $cleanEmail = filter_var($email, FILTER_SANITIZE_EMAIL);
        $cleanMessage = filter_var($msg, FILTER_SANITIZE_STRING);
        } else {
         $app->redirect('/contact');
        }

       $transport = Swift_SendmailTransport::newInstance('/usr/sbin/sendmail -bs');
       $mailer = \Swift_Mailer::newInstance($transport);

        $message = \Swift_Message::newInstance();
        $message->setSubject('Email from our website');
        $message->setFrom(array(
        $cleanEmail => $cleanName
         ));
         $message->setTo(array('treehouse@localhost'));
          $message->setBody($cleanMessage);

        $result = $mailer->send($message);

         if($result > 0) {
         $app->redirect('/');
        } else {
           $app->redirect('/contact');
         }

        });


       $app->run();