如何调用div form到PHP邮件函数？

<div id="myForm">
  <form>
    <label for="email">收件人邮箱：</label>
    <input type="email" id="email" name="email" required><br><br>
    <label for="subject">主题：</label>
    <input type="text" id="subject" name="subject" required><br><br>
    <label for="message">消息：</label>
    <textarea id="message" name="message" required></textarea><br><br>
    <button onclick="sendEmail()">提交</button>
  </form>
</div>

<script>
function sendEmail() {
  // 获取表单数据
  var email = document.getElementById('email').value;
  var subject = document.getElementById('subject').value;
  var message = document.getElementById('message').value;

  // 使用AJAX技术将表单数据发送给后端PHP代码
  var xhr = new XMLHttpRequest();
  xhr.open('POST', 'send_email.php', true);
  xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
      alert(xhr.responseText);  // 显示后端返回的响应信息
    }
  };
  xhr.send('email=' + email + '&subject=' + subject + '&message=' + message);
}
</script>

<?php
$email = $_POST['email'];
$subject = $_POST['subject'];
$message = $_POST['message'];

// 调用PHP邮件函数发送邮件
$headers = "From: your_email@example.com";
mail($email, $subject, $message, $headers);

echo "邮件发送成功！";
?>