如何将电子邮件附加到python 3中顶级邮件内容类型消息/rfc822所在的另一封电子邮件？

from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.mime.image import MIMEImage
from email.mime.audio import MIMEAudio
from email.mime.base import MIMEBase
from email import encoders

msg = MIMEMultipart()

text = MIMEText("这是邮件的正文内容。")

msg.attach(text)

attachment = open("文件路径", "rb")
part = MIMEBase("application", "octet-stream")

part.set_payload(attachment.read())

encoders.encode_base64(part)
part.add_header("Content-Disposition", "attachment", filename="附件文件名")

msg.attach(part)

import smtplib

# 设置邮件服务器和端口
server = smtplib.SMTP("邮件服务器地址", 端口号)

# 登录邮箱账号
server.login("邮箱账号", "邮箱密码")

# 发送邮件
server.sendmail("发件人邮箱", "收件人邮箱", msg.as_string())

# 关闭连接
server.quit()