在linux上用python 2.6发带附件的邮件，正文、附件中文乱码

闪电邮打开正文，中文显示正常。
微信的腾讯企业邮打开正文，中文是乱码。

正文用：
MIMEText(body, 'plain', 'utf-8')

附件用：
        data = open(file_name, 'rb')
        part.set_payload(data.read().decode('utf-8').encode('gbk'))

#!/usr/bin/env python2.6
#coding: utf-8
# Filename: Email.py
# FileDesc: 发送邮件功能

import smtplib
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
from email.MIMEBase import MIMEBase
from email import Encoders
import time
import datetime

test_mailto=["[e-mail]","[e-mail]"]

def send_mail(mailto, body, subject, mail_user="linkwin",
    mail_pwd="Linkwinisbest1", user_alias="linkwin",
    mail_server="smtp.exmail.qq.com", mail_postfix="richba.com", format='plain'):
    sender = mail_user+"@"+mail_postfix
    send_mail_with_file(mailto,body,subject,format,sender,mail_user,mail_pwd, user_alias,mail_server)

def send_mail_with_file( mailto, body, subject, format='plain',
    sender="[e-mail]", user="linkwin",
    password="Linkwinisbest1", user_alias="linkwin",
    mail_server="smtp.exmail.qq.com", appendix=[] ):
    msg = MIMEMultipart()
    msg["to"] = ";".join(mailto)
    msg["from"] = user_alias+"<"+sender+">"
    msg["subject"] = subject

    body_msg = MIMEText(body, format, 'utf-8')
    msg.attach(body_msg)

    ctype='application/octet-stream'
    maintype,subtype = ctype.split('/',1)
    for file_name in appendix:
        part = MIMEBase(maintype, subtype)
        data = open(file_name, 'rb')
        part.set_payload(data.read().decode('utf-8').encode('gbk'))
        data.close()
        Encoders.encode_base64(part)
        part["Content-Type"] = ctype
        desc = "attachment; filename=\"%s\"" % file_name.split("/")[-1]
        part["Content-Disposition"] = desc
        msg.attach(part)
    try:
        print("[begin to send mail ] [from:",sender,"] [to:",mailto,"] [subject:",subject,"]")
        server =smtplib.SMTP(mail_server)
        server.login(sender, password)
        msg["Accept-Language"]="zh-CN"
        msg["Accept-Charset"]="ISO-8859-1,gb2312"
        server.sendmail(sender, mailto, msg.as_string())
        server.quit()
        print("[send mail ok! ] [from:",sender,"] [to:",mailto,"] [subject:",subject,"]")
        return True
    except Exception as e:
        print("send_mail_with_file exception: ",str(e))
        return False

def test_with_attach():
    print("begin to send a mail with attach.")
    today = time.strftime("%Y-%m-%d", time.localtime())
    mailto = test_mailto
    subject = "[attach][测试邮件，有乱码吗?][%s]"%(today)
    body="%s: 测试邮件，有乱码吗?" % (today)
    appendix="../hk/csv/origion_hk_factor_201601260100.csv"
    send_mail_with_file(mailto, body, subject, appendix=[appendix],user_alias="python_email")

def test_no_attach():
    print("begin to send a mail with attach.")
    today = time.strftime("%Y-%m-%d", time.localtime())
    mailto = test_mailto
    subject = "[no attach][测试邮件，有乱码吗?][%s]"%(today)
    body="%s: 测试邮件，有乱码吗?" % (today)
    send_mail(mailto, body, subject)

if __name__ == '__main__':
    open_log("./test.log")
    print("begin to test Email.")
    test_with_attach()
    #test_no_attach()

2.6的print不好用，自己改。