'Initialize the connection to Mailgun.'

def initialize_client(self):

    from pymailgunner import Client
    self._client = Client(self._api_key, self._domain, self._sandbox)
    _LOGGER.debug('Mailgun    domain:    %s', self._client.domain)
    self._domain = self._client.domain
    if (not self._sender):
        self._sender = DEFAULT_SENDER.format(domain=self._domain)
