public function prepareAttachment($attachment)
    {
        if ($this->isFile($attachment) !== true) {
            return false;
        }
        //http://php.net/manual/en/class.finfo.php
        $fileInfo = new \finfo(FILEINFO_MIME_TYPE);
        $fileType = $fileInfo->file($attachment);
        $file = fopen($attachment, 'r');
        $fileContent = fread($file, filesize($attachment));
        $fileContent = chunk_split(base64_encode($fileContent));
        fclose($file);
        $msgContent = 'Content-Type: '.$fileType.'; name='.basename($attachment)."\r\n";
        $msgContent .= 'Content-Transfer-Encoding: base64'."\r\n";
        $msgContent .= 'Content-ID: <'.basename($attachment).'>'."\r\n";
        $msgContent .= "\r\n".$fileContent."\r\n\r\n";

        return $msgContent;
    }