What is OST file ?
An OST file (.ost) is an offline folder file in Microsoft Outlook. Offline folders make it possible for the user to work offline and then to synchronize changes with the Exchange Server the next time they connect. The ability to work offline is useful in environments with limited or unreliable connectivity.
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. Also, if you specify a new folder location for the offline Outlook Data File (.ost), a new file is automatically created. Although not required, you can manually move the existing file to the new folder to avoid the download time that is required to recreate the file.
Use of OST file
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. This type of data file is also used for accounts that you set up with the Outlook Connector for Outlook.com.
How to access OST file
Outlook saves backup information in a variety of different locations. Depending on what type of account you have, you can back up your emails, your personal address book, your navigation pane settings, your signatures, templates, etc.
In order to view some of the backup files for Outlook, you’ll need to unhide system folders and file name extensions.
How to unhide folders and file name extensions
Some of the folders might be hidden folders, and Windows might hide extensions for known files of particular type(.ost).
Following are steps to make extensions and folders visible:
1. Open Control Panel.
For Windows 10- Right-click the Start button, and then click Control Panel.
For Windows 8- Press the Windows key + X, then click Control Panel.
For Windows 7- Click Start>Control Panel.
2. In the View by list, make sure either Large icons or Small icons is selected so that you can see all the icons in Control Panel.
3. Click Folder Options. Click the View tab.
4. In Advanced settings box, under Files and Folders, uncheck the ‘Hide extensions for known file types’ box. Under ‘Hidden files and folders’, click the ‘Show hidden files’, folders, and drives button. Click OK.
Now you can see all folders and extensions of all files. By searching the extension you can find .ost file. Following are locations of .ost file in various windows versions:
Windows 7 and Windows Vista- drive:\Users\user\AppData\Local\Microsoft\Outlook
drive:\Documents and Settings\user\Local Settings\Application Data\Microsoft\Outlook
Some older versions of Windows- drive:\Documents and Settings\<username>\Local Settings\Application Data\Microsoft\Outlook