def send_unsent(self):
        for i in range(len(self.unsent)):
            recipients, msg_string = self.unsent.pop(i)
            self._attempt_send(recipients, msg_string)
Emails that were not being able to send will be stored in self.unsent.
dataset/ETHPy150Open kootenpv/yagmail/yagmail/yagmail.py/SMTP.send_unsent