php email problem -  html / plain text with attachment

<?php
$name=$_POST['name'];
$email=$_POST['email'];
$producter=$_POST['product'];
$message=$_POST['message'];
 
//define the receiver of the email 
$to = $email;
//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: admin@poolexpress.com.au\r\nReply-To: admin@poolexpress.com.au"; 
//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('Zodiac_Tri_Web.pdf'))); 
//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: pdf; name="Zodiac_Tri_Web.pdf"  
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 ) or die ("Mail failed."); 
//if the message is sent successfully print "Mail sent". Otherwise print "Mail failed" 
?>