function _list_mailboxes($root='', $filter='*')
  {
  $a_defaults = $a_out = array();
  
  // get cached folder list  
  $a_mboxes = $this->get_cache('mailboxes');
  if (is_array($a_mboxes))
   return $a_mboxes;

  // retrieve list of folders from IMAP server
  $a_folders = iil_C_ListSubscribed($this->conn, $this->_mod_mailbox($root), $filter);
  
  if (!is_array($a_folders) || !sizeof($a_folders))
   $a_folders = array();

  // create Default folders if they do not exist
  global $CONFIG;

  foreach ($CONFIG['default_imap_folders'] as $folder)
   {
   if (!in_array_nocase($folder, $a_folders))
    {
    $this->create_mailbox($folder, TRUE);
    $this->subscribe($folder);
    }
   }

  $a_folders = iil_C_ListSubscribed($this->conn, $this->_mod_mailbox($root), $filter);
  $a_mailbox_cache = array();

  if (!in_array("INBOX", $a_folders)){
    array_unshift($a_folders, "INBOX");
	$this->subscribe("INBOX");
  }

  // write mailboxlist to cache
  $this->update_cache('mailboxes', $a_folders);
  
  return $a_folders;
  }