防止 php 网络联系表单垃圾邮件

我是一个业余的网页设计师，我在 stackoverflow.com 和其他网站上搜索过，并找到了许多针对我遇到的这个问题的修复程序，但是它们都没有工作（可能是因为我错误地实现了它们）。我希望有更多知识的人可以帮助我进行简单的修复，或者向我展示如何实现我发现的修复程序之一。

问题：我在我的企业网站上有一个非常简单的php联系表格。多年来，它一直运行良好，但在上周已被黑客入侵。我现在每天收到数百份联系表单提交，没有评论，它们只有（显然有效的）电子邮件地址，以及名称字段中的一串字符（如“58ee8b52eef46”）。

我已经尝试了几种技术来防止这种垃圾邮件，它们要么破坏了我的php表单，要么没有阻止垃圾邮件。如果可能的话，我想要一个不需要验证码扭曲文本测试的解决方案，并且不需要填写表单的所有字段。

这是我的完整PHP代码：

<?php
if(isset($_POST['email'])) {
  $email_to = "myemail@example.com";
  $email_subject = "website form submission";

  function died($error) {
    echo "We are very sorry, but there were error(s) found with the form you submitted. ";
    echo "These errors appear below.<br /><br />";
    echo $error."<br /><br />";
    echo "Please go back and fix these errors.<br /><br />";
    die();
  }

  if (!isset($_POST['name']) ||
    !isset($_POST['email']) ||
    !isset($_POST['telephone']) ||
    !isset($_POST['comments'])) {
    died('We are sorry, but there appears to be a problem with the form you submitted.');       
  }

  $name = $_POST['name'];
  $email_from = $_POST['email'];
  $telephone = $_POST['telephone'];
  $comments = $_POST['comments'];

  $error_message = "";
  if(strlen($error_message) > 0) {
    died($error_message);
  }
  $email_message = "Form details below.\n\n";

  function clean_string($string) {
    $bad = array("content-type","bcc:","to:","cc:","href");
    return str_replace($bad,"",$string);
  }

  $email_message .= "Name: ".clean_string($name)."\n";
  $email_message .= "Email: ".clean_string($email_from)."\n";
  $email_message .= "Telephone: ".clean_string($telephone)."\n";
  $email_message .= "Comments: ".clean_string($comments)."\n";

  $headers = 'From: '.$email_from."\r\n" .
             'Reply-To: '.$email_from."\r\n" .
             'X-Mailer: PHP/' . phpversion();
  @mail($email_to, $email_subject, $email_message, $headers);  
?>

Thank you for contacting us. We will be in touch with you soon. You will now be redirected back to example.com.
<META http-equiv="refresh" content="2;URL=http://www.example.com">

<?php
}
die();
?>