The desktop Outlook app uses two types of data files to store local copies of your emails, calendars, contacts, and other items, to allow you access to your information without an internet connection.

If you're using an Outlook.com, Outlook 365, or Exchange account, this information is stored in an Offline Outlook Data File using a .ost format. However, if you're using a POP or IMAP account like those you get from an Internet Service Provider (ISP), your information will be stored in an Outlook Data File using a .pst format instead.

Typically, you can go for a long time without any problems, but sooner or later, these files may stop working, and they can get damaged, which is why Outlook includes the Inbox Repair tool to diagnose and repair common errors with .pst files, as well as a mechanism to recreate .ost files automatically.

In this Windows 10 guide, we walk you through the steps to repair the data files when they're damaged, items are missing in your inbox, or when a data file just won't open in Outlook 2016 or previous versions.

How to fix an Offline Outlook Data File (.ost)

If you have an Outlook.com, Outlook 365, or Exchange account, you can follow these steps to fix problems with a .ost data file in Outlook:

  1. Close Outlook.
  2. Open Control Panel.

    • Quick Tip: If you're only using the default profile named "Outlook," you can use the path %LOCALAPPDATA%\Microsoft\Outlook to go directly to the location of the .ost file, and then jump to step No. 13. Otherwise, continue with the steps below.
  3. Click on User Accounts.
  4. Click on Mail.

  5. Using the Mail Setup experience, click the Show Profiles button.

  6. Select the profile with the account you want to fix. (In Outlook 2016 the default profile is called "Outlook.")
  7. Click the Properties button.

  8. Click the Email Accounts button.

  9. Click on the Data Files tab.
  10. Select the account to be repaired.
  11. Click the Open File Location button.

  12. Before you continue, make sure to close the "Accounts Settings," "Mail Setup," and "Mail" windows.
  13. Right-click the .ost file for the account with problems, and select Delete.

Once you complete these steps, open Outlook again to automatically create a new .ost files for that particular account.

How to fix an Outlook Data File (.pst)

If you have an account connected using POP or IMAP settings, you can use the following steps to fix problems with a .pst data file:

  1. Close Outlook.
  2. Open File Explorer (Windows key + E).
  3. Browse the following path:

    C:\Program Files (x86)\Microsoft Office\root\Office16

    • Important: If you're using Outlook 2013, use the path C:\Program Files (x86)\Microsoft Office\Office15. If you have an older version of the app, change "Office15" in the path to "Office14" for Outlook 2010, or to "Office13" for Outlook 2007.
  4. Inside the folder, find and double-click the SCANPST.EXE file.

  5. Click the Browse button and locate the .pst file you want to repair.
  6. Click the Start button.

  7. Click the Repair button.

Once you complete these steps, the wizard will create a backup, proceed with the repair and create a log file with information about the repair process.

After the repair is complete, you can start the Outlook app associated with the data file.

Additional recovery instructions

While Microsoft's tool can diagnose and repair many problems with a .pst file, the recovery process may require additional steps to get all your items.

For example, after the process, you may find that some of the recreated folders in your inbox are empty. If this is the case, you may also see a Recovered Personal Folders or Lost and Found folder in the left pane. These folders will contain the items that have been repaired but couldn't be restored.

To get these items back, do the following:

  1. Open the Recovered Personal Folders or Lost and Found folder.
  2. Select the items you want to recover.
  3. Drag and drop those items into the correct folders.
  4. Delete the now empty folders.

If there are still items missing, you can use the .pst backup file to recover those additional items using the built-in Import/Export tool:

  1. Select the .bak file located in the same folder that contains the .pst file.
  2. Press the F2 key and rename the file to .bak.pst and press Enter.

  3. Open Outlook.
  4. Click on File.
  5. Click on Open & Export.
  6. Click the Import/Export button.

  7. Select the Import from another program or file option.
  8. Click Next.

  9. Select the Outlook Data File (.pst) option.

  10. Click Next.
  11. Specify the location of the .pst file.
  12. Select the import option.
  13. Click Next.

  14. Select the items you want to import.
  15. Click Finish.

After completing these steps, you should be able to use Outlook with all your data normally.

While this guide focuses on Outlook 2016, you can refer to these instructions to fix the data files on Outlook 2013, 2010, and 2007.

More Windows 10 resources

For more helpful articles, coverage, and answers to common questions about Windows 10, visit the following resources: