What is an index.dat?
An index.dat file is a hidden file that contains a record of every web site address you have ever visited and holds information on all your Internet activities,
yes including emails sent and received through Outlook or Outlook Express One of these files can be located and viewed by Windows Explorer but none can be deleted using either Windows Explorer According to Microsoft these files are used to help speed up the loading of web pages in Internet Explorer. This doesn’t appear to be the case because when you delete the Temporary Internet Files the “index.dat” files remain behind and continue to grow. If you delete or clear the Temporary Internet Files then there is no need to index the URL cache because the files no longer exist. Upload Files