Can't send message

<?php
require 'vendor/autoload.php';
date_default_timezone_set("Europe/London");

//$log = new Logger('name');
//$log->pushHandler(new StreamHandler('app.txt', Logger::WARNING));
//$log->addWarning('Oh Noes.');

// Instantiate new Slim application
$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($email) && !empty($msg)) {
    $cleanName = filter_var($name, FILTER_SANITIZE_STRING);
    $cleanEmail = filter_var($email, FILTER_SANITIZE_EMAIL);
    $cleanMsg = filter_var($msg, FILTER_SANITIZE_STRING);
  } else {
    //tell the user there was a problem
    $app->redirect("/contact");
  }

  //error reported on next line
  $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"));
  $message->setBody($cleanMsg);

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

  if (result > 0) {
    //send thank-you message
    $app->redirect("/");
  } else {
    //send message to user that message failed to send
    //log an error
    $app->redirect("/contact");
  }
});

// Run Slim application
$app->run();