Отправить прикрепленный PDF-файл по электронной почте с помощью PHP с использованием FPDF

Я хочу отправить по электронной почте PDF-файл как вложение, созданное с помощью FPDF. Мой код выглядит так, но вложение никогда не приходит.

<?php
require('lib/fpdf/fpdf.php');

$pdf = new FPDF('P', 'pt', array(500,233));
$pdf->AddFont('Georgiai','','georgiai.php');
$pdf->AddPage();
$pdf->Image('lib/fpdf/giftcertificate.jpg',0,0,500);
$pdf->SetFont('georgiai','',16);
$pdf->Cell(40,10,'Hello World!');
$doc = $pdf->Output('test.pdf', 'S');

//define the receiver of the email
$to = 'myemail@example.com';
//define the subject of the email
$subject = 'Test email with attachment';
//create a boundary string. It must be unique
//so we use the MD5 algorithm to generate a random hash
$random_hash = md5(date('r', time()));
//define the headers we want passed. Note that they are separated with \r\n
$headers = "From: reply@test.com\r\nReply-To: reply@test.com";
//add boundary string and mime type specification
$headers .= "\r\nContent-Type: multipart/mixed; boundary=\"PHP-mixed-".$random_hash."\"";
//read the atachment file contents into a string,
//encode it with MIME base64,
//and split it into smaller chunks
$attachment = chunk_split(base64_encode(file_get_contents($doc)));
//define the body of the message.
ob_start(); //Turn on output buffering
?>
--PHP-mixed-<?php echo $random_hash; ?> 
Content-Type: multipart/alternative; boundary="PHP-alt-<?php echo $random_hash; ?>"

--PHP-alt-<?php echo $random_hash; ?> 
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit

Hello World!!!
This is simple text email message.

--PHP-alt-<?php echo $random_hash; ?> 
Content-Type: text/html; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit

<h2>Hello World!</h2>
<p>This is something with <b>HTML</b> formatting.</p>

--PHP-alt-<?php echo $random_hash; ?>--

--PHP-mixed-<?php echo $random_hash; ?> 
Content-Type: application/zip; name="attachment.zip" 
Content-Transfer-Encoding: base64 
Content-Disposition: attachment 

<?php echo $attachment; ?>
--PHP-mixed-<?php echo $random_hash; ?>--

<?php
//copy current buffer contents into $message variable and delete current output buffer
$message = ob_get_clean();
//send the email
$mail_sent = @mail( $to, $subject, $message, $headers );
//if the message is sent successfully print "Mail sent". Otherwise print "Mail failed"
echo $mail_sent ? "Mail sent" : "Mail failed"; 

?>

Кто-нибудь знаком с этим? Я надеюсь использовать функцию PHP mail ().