python 用邮箱服务器IP'10.188.128.188'发送邮件报错SMTPServerDisconnected

Question

python 发送邮件，报错 raise SMTPServerDisconnected('please run connect() first')

SMTPServerDisconnected: please run connect() first
用邮箱服务器地址报错。
由于邮箱服务器发送文件没有设置账号密码 所以没写，请问哪里有问题呢？

    msg = MIMEMultipart()
    #邮件正文
    msg.attach(MIMEText(mail_body, 'plain', 'utf-8'))
    msg['Subject'] = Header(subject, 'utf-8')
    msg['From'] = username 
    msg['To'] = receiver #

    #附件:附件名称用英文
    #for file_name in file_names:
    att = MIMEText(open(file_name, 'rb').read(), 'base64', 'utf-8')
    att["Content-Type"] = 'application/octet-stream'
    att['Content-Disposition'] = 'attachment;filename="%s"' % (file_name)
    msg.attach(att)
        
    # 服务器准备，登录并发送邮件
    try:
        #smtp = smtplib.SMTP()
        #smtp = smtplib.SMTP_SSL(mail_host,465)
        smtp = smtplib.SMTP()
        smtp.connect('10.188.128.188')
        #smtp.login(username, password)
        smtp.sendmail(sender, receiver.split(','), msg.as_string())
    except Exception as e:
        print(e)
        print("邮件发送失败！")
    else:
        print("邮件发送成功！")
    finally:
        smtp.quit()

print(__name__)

if __name__ == '__main__':
    
    subject="Alarm Report"
    mail_body="测试本文"
    receiver="[e-mail],[e-mail]" #"邮箱1,邮箱2" 接收人邮件地址 sep= ","
    file_name='PPT_SendMail.py'
    sendEmail(subject, mail_body, receiver,file_name)#file_names