public function addHeaderOb(Horde_Mime_Headers_Element $ob, $check = false)
    {
        if ($check) {
            $cname = $this->_getHeaderClassName($ob->name);
            if (!($ob instanceof $cname)) {
                throw new InvalidArgumentException(sprintf(
                    'Object is not correct class: %s',
                    $cname
                ));
            }
        }

        /* Existing header? Add to that object. */
        if ($hdr = $this[$ob->name]) {
            $hdr->setValue($ob);
        } else {
            $this->_headers[$ob->name] = $ob;
        }
    }