发现网站不能注册新用户，报错提示：(550, b’The “From” header is missing or invalid. Please follow RFC5322, RFC2047, RFC822 standard protocol. https://service.mail.qq.com/detail/124/995.')

  定位是注册时不能发邮件验证导致。QQ邮箱的From格式变更，需改为：昵称+空格+<邮箱地址>形式，注意有空格。（原文）

 原代码：
 message['From'] = Header(fromName, 'utf-8')
 改为：
 message['From'] = Header('nickname <abc@qq.com>')
 
 #若发件人fromName含中文，则需要base64转码
 message['From'] = Header('"=?utf-8?B?UVHpgq7nrrHmmLXnp7DnpLrkvos=?=" <abc@qq.com>')

  先将汉字转为bytes，再bytes转base64。此时还是报错(550, b’The mail may contain inappropriate words or content.‘)，一直调试发现转完的base64格式字符串是b’xxxx’形式，还需要将b’xxxx’转为’xxxx’。
  以为这就完了吗，拼接邮箱名称和邮箱地址时fromNamestr打印出来总是少一截，邮箱地址不能显示。不是空格，不是转义字符的问题，是最后的右尖括号，需要用双引号来包裹！

本以为只是小问题，最后花了好几个小时才搞定，总结一个给大家避坑吧。完整代码如下：

import base64
def send_mail(receivers,content,fromName,toName,subject,type='plain'):
    message = MIMEText(content, type, 'utf-8')
  	#汉字转base64
    fromName64 = base64.b64encode(bytes(fromName, 'utf-8')) 
    #b'xxxx'转为'xxxx'
    fromName64str = str(fromName64,'utf-8') 
    #尖括号拼接用双引号
    fromNamestr = '"=?utf-8?B?' + fromName64str + '=?=" <' + sender + ">"
    message['From'] = Header(fromNamestr)
    #
    message['To'] = Header(toName, 'utf-8')
    message['Subject'] = Header(subject, 'utf-8')
    try:
        smtpObj = smtplib.SMTP_SSL(host=mail_host)
        smtpObj.connect(mail_host, 465)  # 25 为 SMTP 端口号
        smtpObj.login(mail_user, mail_pass)
        smtpObj.sendmail(sender, receivers, message.as_string())
        return True
    except smtplib.SMTPException:
        return False