Emails that were not being able to send will be stored in :attr:`self.unsent`.
        Use this function to attempt to send these again

def send_unsent(self):
        """
        Emails that were not being able to send will be stored in :attr:`self.unsent`.
        Use this function to attempt to send these again
        """
        for i in range(len(self.unsent)):
            recipients, msg_string = self.unsent.pop(i)
            self._attempt_send(recipients, msg_string)