'Called by ``message_process`` when a bounce email (such as Undelivered
Mail Returned to Sender) is received for an existing thread. The default
behavior is to check is an integer  ``message_bounce`` column exists.
If it is the case, its content is incremented.
:param mail_id: ID of the sent email that bounced. It may not exist anymore
but it could be usefull if the information was kept. This is
used notably in mass mailing.
:param RecordSet partner: partner matching the bounced email address, if any
:param string email: email that caused the bounce'

@api.multi
def message_receive_bounce(self, email, partner, mail_id=None):

    if ('message_bounce' in self._fields):
        for record in self:
            record.message_bounce = (record.message_bounce + 1)
