Something

 define("RETURNADDRESS", (substr(SITEURL, -1) == "/" ? SITEURL."signup.php?activate.".$id.".".$key : SITEURL."/signup.php?activate.".$id.".".$key));

                        $message = LAN_403.RETURNADDRESS.LAN_407." ".SITENAME."\n".SITEURL;

                        require_once(e_HANDLER."mail.php");
                        if(file_exists(THEME."emails.php")){
                            require_once(THEME."emails.php");
                            $message = ($SIGNUPEMAIL)? $SIGNUPEMAIL:$message;
                        }
                        sendemail($_POST['email'], LAN_404." ".SITENAME, $message);