public function setBodyText($txt, $charset = null, $encoding = Zend_Mime::ENCODING_QUOTEDPRINTABLE)
    {
        if ($charset === null) {
            $charset = $this->_charset;
        }

        $mp = new Zend_Mime_Part($txt);
        $mp->encoding = $encoding;
        $mp->type = Zend_Mime::TYPE_TEXT;
        $mp->disposition = Zend_Mime::DISPOSITION_INLINE;
        $mp->charset = $charset;

        $this->_bodyText = $mp;

        return $this;
    }