How do I get these strange characters when I try to “echo” the html string?

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$to = '[email protected]';
$subject = 'Invoice';
$random_hash = md5(date('r', time()));
$headers = "From: [email protected]: [email protected]";
$headers .= "rnContent-Type: multipart/mixed; boundary="PHP-mixed-".$random_hash.""";
$body=rtrim(chunk_split(base64_encode($body)));
//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="UTF-8"
Content-Transfer-Encoding: 7bit

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

--PHP-alt-<?php echo $random_hash; ?>
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: 7bit

Text Emailu.

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

--PHP-mixed-<?php echo $random_hash; ?>
Content-Type: text/html; charset="UTF-8"; name="faktura.html"
Content-Transfer-Encoding: base64
Content-Disposition: attachment

<?php echo htmlentities($body); ?>
--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 );