登录邮箱，发送msg到指定联系人

        :param to: str: 收件人邮箱
        :param subject: str: 主题
        :param content: str: 内容
        :param files:  list: 附件列表
        :return: None

def send_email(self, to, subject, content, files=None):
        """登录邮箱，发送msg到指定联系人

        :param to: str: 收件人邮箱
        :param subject: str: 主题
        :param content: str: 内容
        :param files:  list: 附件列表
        :return: None
        """
        msg = EmailSender._construct_msg(self, to, subject, content, files=files)
        try:
            self.smtp.sendmail(self.from_, to, str(msg))
        except:
            self.login()
            self.smtp.sendmail(self.from_, to, str(msg))