python3 新式邮件写法 附件乱码 解决

import sys
import re
import mimetypes
import base64
import traceback
from pathlib import PurePath
from datetime import date
from calendar import monthrange

import smtplib
from email.headerregistry import Address, Group
from email.utils import localtime, make_msgid
from email.message import EmailMessage

邮件服务器 = "smtp.exmail.qq.com"
邮件服务器_端口 = 465
发送者账号 = "public@qq.com"
发送者密码 = "Admin"
发送者昵称 = "公司"



def get_type(path):
    ctype, encoding = mimetypes.guess_type(path)
    if ctype is None or encoding is not None:
        ctype = 'application/octet-stream'
    return ctype.split('/', 1)


def dd_b64(headstr):
    """对邮件header及附件的文件名进行两次base64编码，防止outlook中乱码。email库源码中先对邮件进行一次base64解码然后组装邮件，所以两次编码"""
    headstr = '=?utf-8?b?' + base64.b64encode(headstr.encode('UTF-8')).decode() + '?='
    headstr = '=?utf-8?b?' + base64.b64encode(headstr.encode('UTF-8')).decode() + '?='
    return headstr


def make_msg(to_name, to_addrs, html_table):
    msg = EmailMessage()
    msg['From'] = Address(dd_b64(发送者昵称), addr_spec = 发送者账号)  # 省略addr_spec会出现 由 xxx 代发
    msg['To'] = Address(dd_b64(to_name), addr_spec = to_addrs)
    msg['Subject'] = 邮件主题
    msg['Date'] = localtime()

    msg_cid = make_msgid()
    html_table = html_table.replace('</body>', f'<img src="cid:{msg_cid[1:-1]}" width="300"/></body>')
    msg.add_alternative(html_table, subtype = 'html')
    # msg.set_content(html_table,subtype = 'html')
    path = r"E:\OneDrive\图片\壁纸\forests2.jpg"
    with open(path, 'rb') as img:
        msg.get_payload()[0].add_related(img.read(), *get_type(path), cid = msg_cid)

    path = r"C:\Users\sharp\Desktop\新建 Microsoft Excel 工作表.xlsx"
    with open(path, 'rb') as fi:
        msg.add_attachment(fi.read(), *get_type(path), filename = dd_b64(PurePath(path).name))

    return msg


server = smtplib.SMTP_SSL(邮件服务器, 邮件服务器_端口)
server.login(发送者账号, 发送者密码)
server.send_message(msg)

解决乱码的中心就是先两次base64，原因在代码的注释中。