function convert_email_adr($email) {
    $pieces = str_split(trim($email));
    $new_mail = '';
    foreach ($pieces as $val) {
        $new_mail .= '&#'.ord($val).';';
    }
    return $new_mail;
}

http://www.web-development-blog.com/archives/e-mail-links-protective-solutions-against-spam/

usage:
<?php>

Hide your e-mail address using PHP

email

PHP