PHP – e-mail de texto simples

Como transformar isso em um e-mail de texto simples?

$bound_text=md5(uniqid(time())); $headers.="MIME-Version: 1.0\r\n" . "Content-Type: multipart/mixed; boundary=\"PHP-mixed-$bound_text\"\r\n"; $message="--PHP-mixed-$bound_text\r\n" ."Content-Type: text/html; charset=\"utf-8\"\r\n" ."Content-Transfer-Encoding: 7bit\r\n\r\n" ."" ."
$text_message
\r\n\r\n" ."--PHP-mixed-$bound_text\r\n" ."Content-Transfer-Encoding: base64\r\n" ."Content-Disposition: attachment; filename=\"$attachment\"\r\n" ."Content-Type: image/jpeg; name=\"$attachment\"\r\n\r\n" .chunk_split($file) ."\r\n\r\n" ."--PHP-mixed-$bound_text--\r\n\r\n"; }

É apenas remover a parte HTML e alterar o texto / html em texto / planície ?