Backing Up and Restoring Outlook Data Files (.pst/.ost)

Summary

This guide helps you troubleshoot and resolve: Backing Up and Restoring Outlook Data Files (.pst/.ost). Follow the steps below to fix the issue.

Common Causes

Important Differentiations

• PST file: Contains all mailbox data. Back this up regularly.
• OST file: A local cache of your server mailbox. It is regenerated from the server, so it generally does not need to be backed up. If you lose the server account, the OST file is difficult to convert and should not be used as a primary backup. It can be converted to PST for archiving purposes only.

Prerequisites

• Access to Outlook Account Settings to locate file paths.
• An external drive, network location, or cloud storage for the backup.
• For OST conversion, the Outlook account must be set up and synchronised. See Setting Up an Email Account in Outlook (POP/IMAP/Exchange) for guidance.

Part 1: Backing Up Your Data

Step A: Identifying Your Data File Location

1. Open Outlook.
2. Navigate to File > Account Settings > Account Settings.
3. Double‑click your email account in the list.

4. Note the file path (e.g., C:\Users\YourUser\Documents\Outlook Files\… or a hidden location in AppData).

Step B: Copying the File (Manual Backup)

1. Close Outlook completely. This is vital to unlock the file.
2. Open File Explorer and navigate to the identified path.
3. Copy the .pst or .ost file.
4. Paste it into your secure backup location (e.g., external USB drive).
5. Rename the backup copy to include the date, for example OutlookBackup-20260814.pst.

Step C: Using Outlook’s Export Feature (Alternative)

This creates a new PST file containing selected data. It is useful for archiving or moving to another computer.

1. Open Outlook.
2. Go to File > Open & Export > Import/Export.
3. Select Export to a file and click Next.
4. Choose Outlook Data File (.pst) and click Next.
5. Select the top‑level mailbox (or specific folders) you wish to export.

6. Click Next.
7. Specify a destination and filename for the new PST.
8. Click Finish. You may be prompted to set an optional password.

Part 2: Restoring Data

Scenario 1: Outlook Can’t Open Your Existing File

1. Close Outlook.
2. Locate the backup .pst file you created.
3. Copy the backup file to a reliable location on your computer (internal drive or a stable network share).
4. Open Outlook.
5. Navigate to File > Account Settings > Account Settings.
6. On the Data Files tab, select the broken file and click Remove.
7. Click Add… > Outlook Data File (.pst), then browse to the backup file and select it.
8. Set the restored file as the default data file if desired.
9. Restart Outlook. Your data should now load from the backup.

Scenario 2: Recovering Deleted Items or Old Emails

If you only need specific messages, import them from the backup PST rather than replacing the entire data file.

1. Open Outlook.
2. Go to File > Open & Export > Import/Export.
3. Select Import from another program or file and click Next.
4. Choose Outlook Data File (.pst) and click Next.
5. Browse to your backup file.

6. Click Next.
7. Select the folder within the backup you wish to import (usually the top‑level mailbox).
8. Choose a destination folder in your current mailbox (e.g., a new folder called “Imported Backup”) to keep things organised.
9. Click Finish.

Scenario 3: Recovering a Deleted Account (OST to PST)

If an Exchange or Office 365 account has been removed but the local .ost file remains, follow these steps:

• Outlook cannot directly import an OST file.
• Re‑create the Exchange/Office 365 account in Outlook to regenerate a fresh OST file. See How to add email to Outlook for instructions.
• If you must retain the original data, use a reputable third‑party OST‑to‑PST converter to create a PST, then import the PST as described in Scenario 2.

Best Practices for Data Files

• Regular backups: Automate PST backups using backup software or schedule manual copies weekly.
• File size management: Keep PST files under 20 GB where possible to reduce corruption risk. Use Outlook’s AutoArchive feature (File > Info > Cleanup Tools > AutoArchive) to move older items to a separate archive PST.
• Storage location: Do not store PST files on network drives or roaming profiles, as this can cause corruption. OST files are server caches and should reside on local drives only.

Troubleshooting

• “The file cannot be opened”: Ensure Outlook is fully closed (check Task Manager for OUTLOOK.EXE) and verify file permissions.
• “Not a valid Outlook Data File”: The file is likely corrupted. Run SCANPST.EXE (see KB‑012 – Using the Outlook Repair Tool) on the file.
• Prompt for password: If a password was set during export, you must enter it to open the PST.

When to Seek Further Assistance

If the PST file is severely corrupted (SCANPST fails or hangs) and you have no viable backup, you may need specialised data‑recovery services or third‑party repair software. Open a Ticket for further help.

Still Having Issues?