The postinfo.html file is necessary for the frontpage extensions. However, if your files are updated through FTP, you don't need the FrontPage Extensions. You can then delete (if present) the '_private', '_vti_bin', '_vti_cnf', '_vti_log', '_vti_pvt', '_vti_txt' directories on your website and the '_vti_inf.html' and 'postinfo.html' files