public function getHeader($name, $format = null)
    {
        if ($this->_headers === null) {
            $this->getHeaders();
        }

        $lowerName = strtolower($name);

        if ($this->headerExists($name) == false) {
            $lowerName = strtolower(preg_replace('%([a-z])([A-Z])%', '\1-\2', $name));
            if($this->headerExists($lowerName) == false) {
                /**
                 * @see Zend_Mail_Exception
                 */
                // require_once 'Zend/Mail/Exception.php';
                throw new Zend_Mail_Exception("no Header with Name $name or $lowerName found");
            }
        }
        $name = $lowerName;

        $header = $this->_headers[$name];

        switch ($format) {
            case 'string':
                if (is_array($header)) {
                    $header = implode(Zend_Mime::LINEEND, $header);
                }
                break;
            case 'array':
                $header = (array)$header;
            default:
                // do nothing
        }

        return $header;
    }