Outlook Data Files (.ost) are always copies of items that are saved on a mail server and don’t need to be backed up like Outlook Data Files (.pst). This type of data file is also used for accounts that you set up with the Outlook Connector for (formerly Hotmail). Outlook Data Files (.ost) are used when you have an Exchange account and want to work offline or use or use the default Cached Exchange Mode. Although not required, you can manually move the existing file to the new folder to avoid the download time that is required to re-create the file. Also, if you specify a new folder location for the offline Outlook Data File (.ost), a new file is automatically created.
Note: By default, when you add an account that uses an offline Outlook Data File (.ost), the file is automatically created and data from the server is downloaded.
