'Called by ``message_process`` when a new message is received
for an existing thread. The default behavior is to update the record
with update_vals taken from the incoming email.
Additional behavior may be implemented by overriding this
method.
:param dict msg_dict: a map containing the email details and
attachments. See ``message_process`` and
``mail.message.parse()`` for details.
:param dict update_vals: a dict containing values to update records
given their ids; if the dict is None or is
void, no write operation is performed.'

@api.multi
def message_update(self, msg_dict, update_vals=None):

    if update_vals:
        self.write(update_vals)
    return True
