public function check_mime_extensions()
    {
        $errors = array();
        $types  = array(
            'application/zip'   => 'zip',
            'text/css'          => 'css',
            'application/pdf'   => 'pdf',
            'image/gif'         => 'gif',
            'image/svg+xml'     => 'svg',
        );

        foreach ($types as $mimetype => $expected) {
            $ext = rcube_mime::get_mime_extensions($mimetype);
            if (!in_array($expected, (array) $ext)) {
                $errors[] = array($mimetype, $ext, $expected);
            }
        }

        return $errors;
    }