如何使用facebook php sdk检索facebook用户的朋友电子邮件信息

This is what I tried

if ($user) {
  try {    
  $my_access_token=$facebook->getAccessToken();

  $friends = $facebook->api('/me/friends',array('access_token'=>$my_access_token));
  echo "<pre>";
  print_r($friends);
  echo "</pre>";
  } catch (FacebookApiException $e) {
  echo '<pre>'.htmlspecialchars(print_r($e, true)).'</pre>';
  $user = null;

} }

But this code only return the list of friends & not the friends email id

even after setting the permission like User & Friend Permissions,email in the app configuration.

Any idea?

how to get friend's email addresses

Thanks in advance!