使用smtp从Python发送邮件，手机中无内容

我正在使用Python smtp模块发送邮件，它发送成功，并且在Outlook中看起来不错。到我签到手机时，它没有内容，只有附件。实际上内容中有三个表。有人知道如何解决此问题吗？下面是我的代码。

def send_mail(subject, sender, recipient, cc, toaddrs, body, filename):
    msg = MIMEMultipart('alternative')
    msg['Subject'] = subject
    msg['From'] = sender
    msg['To'] = ", ".join(recipient)
    msg['Cc'] = ", ".join(cc)

    message = MIMEText(body, 'html')  # html.read(), 'html')
    msg.attach(message)
    attachment = MIMEBase('application', 'octet-stream')
    attachment.set_payload(open(filename, 'rb').read())
    encoders.encode_base64(attachment)
    attachment.add_header(
        'Content-Disposition', 'attachment; filename="%s"' % os.path.basename(filename))
    msg.attach(attachment)
    smtp = smtplib.SMTP('localhost')
    smtp.sendmail(sender, toaddrs, msg.as_string())
    logger.info('Email have sent successfully!')
    smtp.quit()

任何帮助将不胜感激。谢谢。