未发送PHP邮件图像附件

需要明确的是，我没有写这段代码，这是以前的开发人员写的。无论如何，我的客户在通过他们的表单上传时没有收到图像，只是一个带有错误消息的红框。

根据请求，这里是完整的代码：

<?php
function sendMail() {
  if (!isset ($_POST['to_email'])) { //Oops, forgot your email addy!
    die ("<p>Oops!  You forgot to fill out the email address! Click on the back arrow to go back</p>");
  }
  else {
    $to_name = stripslashes($_POST['to_name']);
    $from_name = stripslashes($_POST['from_name']);
    $from_telephone = stripslashes($_POST['from_telephone']);
    $subject = stripslashes($_POST['subject']);
    $body = stripslashes($_POST['body']);
    $address = stripslashes($_POST['address']);
    $to_email = $_POST['to_email'];
    $attachment = $_FILES['attachment']['tmp_name'];
    $attachment_name = $_FILES['attachment']['name']; 
    if (is_uploaded_file($attachment)) { //Do we have a file uploaded?
      $fp = fopen($attachment, "rb"); //Open it
      $data = fread($fp, filesize($attachment)); //Read it
      $data = chunk_split(base64_encode($data)); //Chunk it up and encode it as base64 so it can emailed
      fclose($fp);
    }
    //Let's start our headers
    $headers = "From: $from_name<" . $_POST['from_email'] . ">'n";
    $headers .= "Reply-To: <" . $_POST['from_email'] . ">'n"; 
    $headers .= "MIME-Version: 1.0'n";
    $headers .= "Content-Type: multipart/related; type='"multipart/alternative'"; boundary='"----=MIME_BOUNDRY_main_message'"'n"; 
    $headers .= "X-Sender: $from_name<" . $_POST['from_email'] . ">'n";
    $headers .= "X-Mailer: PHP4'n";
    $headers .= "X-Priority: 3'n"; //1 = Urgent, 3 = Normal
    $headers .= "Return-Path: <" . $_POST['from_email'] . ">'n"; 
    $headers .= "This is a multi-part message in MIME format.'n";
    $headers .= "------=MIME_BOUNDRY_main_message 'n"; 
    $headers .= "Content-Type: multipart/alternative; boundary='"----=MIME_BOUNDRY_message_parts'"'n"; 
    $message = "------=MIME_BOUNDRY_message_parts'n";
    $message .= "Content-Type: text/plain; charset='"iso-8859-1'"'n"; 
    $message .= "Content-Transfer-Encoding: quoted-printable'n"; 
    $message .= "'n"; 
    /* Add our message, in this case it's plain text.  You could also add HTML by changing the Content-Type to text/html */
    $message .= "Return call on: $from_telephone'n'n";
    $message .= "$address'n'n";
    $message .= "$body'n";
    $message .= "'n"; 
    $message .= "------=MIME_BOUNDRY_message_parts--'n"; 
    $message .= "'n"; 
    $message .= "------=MIME_BOUNDRY_main_message'n"; 
    $message .= "Content-Type: application/octet-stream;'n'tname='"" . $attachment_name . "'"'n";
    $message .= "Content-Transfer-Encoding: base64'n";
    $message .= "Content-Disposition: attachment;'n'tfilename='"" . $attachment_name . "'"'n'n";
    $message .= $data; //The base64 encoded message
    $message .= "'n"; 
    $message .= "------=MIME_BOUNDRY_main_message--'n"; 
    // send the message
    mail("$to_name<$to_email>", $subject, $message, $headers); 
    print "<p align='"center'">Thank you for your email.</p>";
  }
}
switch ($action) {
  case "send":
    showForm();
    sendMail();
    break;
  default:
    showForm();
}
?>

我完全被这段代码弄糊涂了，因为我没有写它，也无法解密为什么"$attachment_name"answers"$attachement_name"是单独的字符串，如果我把"attachmentname"改为"attachment"，我的问题会得到解决吗？