Multipart mail but no message

PHP
1

I’ve scripted this code to have the email sent both in html text and plain text. Though the email arrives and the from / subject fields are filled in, the message itself remains empty. I also can’t switch from html text to plain text.

Where lies the error?

<?php
// configure boundary string
$semi_rand = md5(time()); 
$mime_boundary = "==Multipart_Boundary_x{$semi_rand}x";

// initialize variables 
$to = 'info@nomessageinmail.nl';
$subject = 'Een vraag';
$from = stripslashes(utf8_decode($_POST['from']));
$email = stripslashes(utf8_decode($_POST['email']));
$comments = stripslashes(utf8_decode($_POST['comments']));

// start multipart message
$message = "This is a MIME encoded message."; 

//This is the text/plain version
$message .= "\\r\
\\r\
--" . $mime_boundary . "\\r\
";
$message .= "Content-type: text/plain;charset=iso-8859-1\\r\
\\r\
";
$message .= 'Van: ' . $from . "\\r\
";
$message .= 'Email: '. $email ."\\r\
";
$message .= 'Bericht: '. $comments;

//This is the text/html version
$message .= "\\r\
\\r\
--" . $mime_boundary . "\\r\
";
$message .= "Content-type: text/html;charset=iso-8859-1\\r\
\\r\
";
$message .= '<b>Van:</b> ' . $from . "\\r\
";
$message .= 'Email: '. $email ."\\r\
";
$message .= 'Bericht: '. $comments;
$message = nl2br($message);

$message .= "\\r\
\\r\
--" . $mime_boundary . "--";

// add additional email headers for more user-friendly reply
$headers = "MIME-Version: 1.0\\r\
";
$headers .= "Content-Type: multipart/alternative;boundary=" . $mime_boundary  . "\\r\
";
$headers .= "From: " . mb_encode_mimeheader($from, "iso-8859-1", "Q") ." <" . $email . ">\\r\
"; 
$headers .= "Reply-To: $email\\r\
";

// send email message
$OK = mail($to, $subject, $message, $headers);
// let Flash know what the result was
if ($OK) {
  echo 'sent=OK';
  }
  else {
  echo 'sent=failed&reason='. urlencode('Er is een probleem met de server. Probeer het later nog eens.');
  }
?>