This article contains the following sections:

How to create an Offline Folder (.OST) file

Outlook 2007/2010/2013/2016/2019

  1. In Outlook 2007: Open the Tools menu.
    In Outlook 2010/2013/2016/2019: Open the File tab on the Ribbon, click Account Settings, and choose Account Settings...
  2. In the Account Settings window select the email account, then double-click it or click Change. 
  3. Click More Settings.
  4. Select Advanced tab, then click Outlook Data File Settings.
    Note: If your Outlook runs in Online mode, the Outlook Data File Settings will be grayed out. To enable it, click the checkbox Use Cached Exchange Mode.
  5. In the File box, type the path to the file that you want to use as the .ost file and click on OK. The default name is Outlook.ost. If this file already exists, you will be prompted for a new name.

    If you see this message, click OK:
    "<path> <filename>.ost could not be found. Would you like to create it?"
    (<path> represents the path to the .ost file and <filename> represents the name of the .ost file.)


    Offline Folder Settings
  6. Click OK, Next, and then click Finish.
    Note: Outlook must be connected to the Exchange server for the initial creation and synchronization of the Offline Folder file. 

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How to compact an Offline Folder (.OST) file

  1. Follow the steps above to get to Offline Folder File Settings.
  2. Click on Compact Now.

CompactNow

Notes:

  • To delete an item from both the online and offline folders, select the item, and then press Delete.
  • If you are using an Exchange Server email account in Cached Exchange Mode, only the selected folder will be cleared from the local .ost file. The items on the server will be downloaded again to the .ost file on the next synchronization if the folder is selected under Folder Options in Send/Receive Settings for the Exchange email account.
  • When you use Cached Exchange Mode, public folder favorites are not synchronized by default. If you choose to synchronize public folders, the size of your Offline Folder file (.ost) may increase significantly.

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How to repair an Offline Folder (.OST) file

If you get error messages when synchronizing your Offline Folder file (.ost) in Outlook with your mailbox on an Exchange Server, use the Inbox repair tool (Scanpst.exe) to check your datafile. 

For step-by-step instructions, please refer to the article How To Use The Inbox Repair Tool (scanpst.exe).

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How to delete an Offline Folder (.OST) file

Sometimes an .ost file becomes corrupted beyond repair or repair is not desirable. In this case, it can be deleted. After it has been deleted, you may need to create a new .ost file in order for Outlook to work properly.

  1. Quit Outlook, if it is running.
  2. From the Start menu, choose Run.
  3. In the Run window, type this path in the Open box and click OK:
    "%LOCALAPPDATA%\Microsoft\Outlook\"
    To find the exact path, follow the steps above to get to Offline Folder File Settings. You can see the .ost file location in the Filebox. You may want to copy and paste that information in the Run window for accuracy and ease.

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