Email PDF Attachment with PHP Using FPDF

I want to email a PDF as an attachment that was created using FPDF. My code looks like this, but the attachment never comes through.

<?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 = '[e-mail]';
//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 rn
$headers = "From: [e-mail]-To: [e-mail]";
//add boundary string and mime type specification
$headers .= "rnContent-Type: multipart/mixed; boundary="PHP-mixed-".$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"; 

?>

Anyone familiar with doing this? I’m hoping to use the PHP mail() function.

Answer

This ended up working for me:

<?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/image.jpg',0,0,500);
$pdf->SetFont('georgiai','',16);
$pdf->Cell(40,10,'Hello World!');

// email stuff (change data below)
$to = "[e-mail]"; 
$from = "[e-mail]"; 
$subject = "send email with pdf attachment"; 
$message = "<p>Please see the attachment.</p>";

// a random hash will be necessary to send mixed content
$separator = md5(time());

// carriage return type (we use a PHP end of line constant)
$eol = PHP_EOL;

// attachment name
$filename = "test.pdf";

// encode data (puts attachment in proper format)
$pdfdoc = $pdf->Output("", "S");
$attachment = chunk_split(base64_encode($pdfdoc));

// main header
$headers  = "From: ".$from.$eol;
$headers .= "MIME-Version: 1.0".$eol; 
$headers .= "Content-Type: multipart/mixed; boundary="".$separator.""";

// no more headers after this, we start the body! //

$body = "--".$separator.$eol;
$body .= "Content-Transfer-Encoding: 7bit".$eol.$eol;
$body .= "This is a MIME encoded message.".$eol;

// message
$body .= "--".$separator.$eol;
$body .= "Content-Type: text/html; charset="iso-8859-1"".$eol;
$body .= "Content-Transfer-Encoding: 8bit".$eol.$eol;
$body .= $message.$eol;

// attachment
$body .= "--".$separator.$eol;
$body .= "Content-Type: application/octet-stream; name="".$filename.""".$eol; 
$body .= "Content-Transfer-Encoding: base64".$eol;
$body .= "Content-Disposition: attachment".$eol.$eol;
$body .= $attachment.$eol;
$body .= "--".$separator."--";

// send message
mail($to, $subject, $body, $headers);

?>