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What is OST File Extension?

OST (.ost) stands for Offline Storage Table, also known as offline storage files in MS Outlook. OST files are the cache copy of an Exchange mailbox generated on the local end to work when the server is unavailable. Therefore, making OST file allows users to work in server downtime conditions which can later be updated to the Exchange Server the next time connection to the network is established. Moreover, OST files are replica of users mailbox stored in Exchange Server Database (EDB file). Everytime the connection to the server is available, the two files get synchronized with each other.

The OST file belongs to the category of Database Files.

All MS Outlook versions

Microsoft Corporation


Hexadecimal: 21 42 44 4e


The default address of OST file extension depends on the MS Outlook versions installed on the user system. For each version, the address will be different:

MS Outlook 2000 and 2003

C:\Documents and Settings\%username%\Local Settings\Application Data\Microsoft\Outlook\

MS Outlook 2007


MS Outlook 2010

C:\Documents and Settings\%username%\My Documents\Outlook Files

MS Outlook 2013

C:\Users\%username%\Documents\Outlook Files

To Open OST File user need to follow following methods

  • Manual Method: Create new OST File and open it using Outlook Data Files Settings. In this method, a new copy of files is created that can be used to view Emails in Outlook OST files.
  • Use freeware tool to open OST File

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