public function addAttachmentPartFromFile($filePath, $mimeType, $filename = null, $disposition = 'attachment')
    {
        $handle = Psr7\stream_for(fopen($filePath, 'r'));
        if ($filename === null) {
            $filename = basename($filePath);
        }
        $this->addAttachmentPart($handle, $mimeType, $filename, $disposition);
    }