无法通过pywin32发送电子邮件

import smtplib
from email.mime.text import MIMEText
from email.header import Header

def send_email():
    # 邮件内容
    mail_content = "这是一封测试邮件。"

    # 构造邮件
    message = MIMEText(mail_content, 'plain', 'utf-8')
    message['From'] = Header("发件人", 'utf-8')
    message['To'] = Header("收件人", 'utf-8')
    message['Subject'] = Header("测试邮件", 'utf-8')

    # SMTP服务器设置
    smtp_server = 'smtp.example.com'
    smtp_port = 25
    username = 'your_email@example.com'
    password = 'your_password'

    # 发送邮件
    try:
        smtp_obj = smtplib.SMTP(smtp_server, smtp_port)
        smtp_obj.login(username, password)
        smtp_obj.sendmail(username, [username], message.as_string())
        print("邮件发送成功")
    except smtplib.SMTPException as e:
        print("邮件发送失败：" + str(e))

# 调用发送邮件函数
send_email()