Flask邮件-无法发送带有附件的邮件

from flask_mail import Mail, Message

app.config['MAIL_SERVER'] = 'smtp.qq.com'  # 邮件服务器地址
app.config['MAIL_PORT'] = 465  # 邮件服务器端口
app.config['MAIL_USE_SSL'] = True  # 启用SSL加密
app.config['MAIL_USERNAME'] = 'your-email@qq.com'  # 发件人邮箱
app.config['MAIL_PASSWORD'] = 'your-email-password'  # 发件人邮箱密码

mail = Mail(app)

msg = Message('邮件主题', sender='your-email@qq.com', recipients=['recipient-email@example.com'])

msg.body = '邮件正文内容'

with app.open_resource('path/to/attachment.pdf') as attachment:
    msg.attach('attachment.pdf', 'application/pdf', attachment.read())

mail.send(msg)