def deliver!(mail)
      mg_message = Railgun.transform_for_mailgun(mail)
      response = @mg_client.send_message(@domain, mg_message)

      if response.code == 200 then
        mg_id = response.to_h['id']
        mail.message_id = mg_id
      end
      response
    end
def deliver!(mail)
      mg_message = Railgun.transform_for_mailgun(mail)
      response = @mg_client.send_message(@domain, mg_message)

      if response.code == 200 then
        mg_id = response.to_h['id']
        mail.message_id = mg_id
      end
      response
    end
Initialize the Railgun mailer.

 @param [Hash] config Hash of config values, typically from `app_config.action_mailer.mailgun_config`