public function move($object_id, $new_folder)
{
if ($this->objectIdExists($object_id)) {
$uid = $this->getBackendId($object_id);
} else {
throw new Horde_Kolab_Storage_Exception(sprintf('No such object %s!', $object_id));
}
$this->_driver->moveMessage($uid, $this->_folder->getPath(), $new_folder);
$this->synchronize(array('changes' => array(Horde_Kolab_Storage_Folder_Stamp::ADDED => array(), Horde_Kolab_Storage_Folder_Stamp::DELETED => array($uid => $object_id))));
}