通过Python发送电子邮件时，文本文件未嵌入到HTML中

import smtplib
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.mime.image import MIMEImage

# 邮件配置
smtp_server = "smtp.example.com"  # 设置SMTP服务器地址
smtp_port = 587  # 设置SMTP服务器端口
smtp_username = "your_email@example.com"  # 设置发件人邮箱账号
smtp_password = "your_email_password"  # 设置发件人邮箱密码

# 构建邮件内容
msg = MIMEMultipart('alternative')
msg['From'] = "sender@example.com"  # 设置发件人
msg['To'] = "recipient@example.com"  # 设置收件人
msg['Subject'] = "HTML邮件示例"  # 设置邮件主题

# 邮件正文内容
text = "这是一封HTML邮件示例。<br>以下是一个嵌入的文本文件：<br>"
text += "<a href='cid:file.txt'>查看文本文件</a>"  # 添加链接

# 将正文内容转换为MIMEText对象并添加到邮件中
msg.attach(MIMEText(text, 'html'))

# 读取文本文件内容并添加为附件
with open("file.txt", "r") as file:
    attachment = MIMEText(file.read())
    attachment.add_header('Content-Disposition', 'attachment', filename="file.txt")
    attachment.add_header('Content-ID', '<file.txt>')
    msg.attach(attachment)

# 连接SMTP服务器并发送邮件
with smtplib.SMTP(smtp_server, smtp_port) as server:
    server.starttls()  # 使用TLS加密连接
    server.login(smtp_username, smtp_password)  # 登录邮箱账号
    server.send_message(msg)  # 发送邮件

print("邮件发送成功")