Как изменить текст письма

. "\n"
                . MAIL_AFFILIATE_USERNAME . $a_email_address . "\n"
                . MAIL_AFFILIATE_PASSWORD . $a_password . "\n\n"
                . MAIL_AFFILIATE_LINK
                . HTTP_SERVER . DIR_WS_CATALOG . FILENAME_AFFILIATE . "\n\n"
                . MAIL_AFFILIATE_FOOTER;

    os_php_mail(AFFILIATE_EMAIL_ADDRESS, STORE_OWNER, $a_email_address, $a_firstname . ' ' . $a_lastname, '', AFFILIATE_EMAIL_ADDRESS, STORE_OWNER, '', '', MAIL_AFFILIATE_SUBJECT, nl2br($aemailbody), nl2br($aemailbody));