'Send an email message using the underlying ``_mailer``.
:param Record rec: a database record from the ``email_queue`` table
:return int: the number of emails sent (0 or 1)'

def _flush_one(self, rec):

    message = self._prepare_email_message_for_ses(rec)
    if (message is None):
        return 0
    self._mailer.send_email(**message)
    return 1
