Python 阿里云服务器使用SMTP协议和25端口发送邮件报SMTPServerDisconnected(“Connection unexpectedly closed“)错误的解决办法

1.发送邮件函数：

import smtplib

def send_mail(trade_date, receivers=None, subject='数据采集完成', content='数据采集完成'):
    mail_host = "smtp.qq.com"
    mail_user = "XXXXXX@qq.com"
    mail_pass = "XXXXXXXXXXXXXXX"
    sender = 'XXXXXX@qq.com'
    receivers = ['XXXXXX@qq.com'] if receivers is None else receivers
    message = MIMEText(content, 'html', 'utf-8')
    message['From'] = Header("YdSoft", 'utf-8')
    message['To'] = Header("YdSoft", 'utf-8')
    message['Subject'] = Header(trade_date + subject, 'utf-8')
    try:
        smtp_obj = smtplib.SMTP()
        smtp_obj.connect(mail_host, 25)
        smtp_obj.login(mail_user, mail_pass)
        smtp_obj.sendmail(sender, receivers, message.as_string())
        smtp_obj.quit()
        print("邮件发送成功！")
    except smtplib.SMTPException:
        print("Error: 邮件发送失败！")

2.问题描述

在本地开发时，上述send_mail（）函数可以正常发送邮件。但部署到阿里云服务器时，出现了问题，报SMTPServerDisconnected("Connection unexpectedly closed")错误：

Traceback (most recent call last):
  File "D:\ydpy\ydtools\get_select_result.py", line 41, in <module>
    d.select()
  File "D:\ydpy\ydtools\get_select_result.py", line 35, in select
    send_mail(self.trade_date, ['XXXXXX@qq.com'], '筛选结果', self.trade_date + '筛选结果为：<br/>' + result)
  File "D:\ydpy\ydtools\func\yd_func.py", line 131, in send_mail
    smtp_obj.connect(mail_host, 25)
  File "D:\Program Files\Python\Python39\lib\smtplib.py", line 343, in connect
    (code, msg) = self.getreply()
  File "D:\Program Files\Python\Python39\lib\smtplib.py", line 400, in getreply
    raise SMTPServerDisconnected("Connection unexpectedly closed")
smtplib.SMTPServerDisconnected: Connection unexpectedly closed

3.原因分析

上述send_mail()使用SMTP协议和25端口发送邮件，但由于smtp的25端口容易收到攻击，所以对于某些云服务器，比如说阿里云服务器，25端口是被禁止的。所以，此时应采用其他可用的端口和协议来发送邮件。

4.解决办法

改用SSL协议和465端口即可解决上述问题，即将send_mail()函数作如下修改：

将：

smtp_obj = smtplib.SMTP()
smtp_obj.connect(mail_host, 25)

改为：

smtp_obj = smtplib.SMTP_SSL(mail_host)
smtp_obj.connect(mail_host, 465)

如此，即可解决无法使用SMTP协议和25端口发送邮件的问题！