Summary

Your Outlook data (emails, contacts, calendar, tasks) is stored in either a .PST (Personal Storage Table) file for POP/IMAP accounts or an .OST (Offline Storage Table) file for Exchange/Office 365 accounts (cached mode). This guide covers how to back up and restore this critical data.

Important Differentiations

• PST File: Contains all mailbox data. Back this up regularly.
• OST File: A local cache of your server mailbox. If you lose the server account, the OST file is difficult to convert and *should not* be used as a primary backup. However, it can be converted to PST for archiving purposes.

Prerequisites

• Access to the Outlook Account Settings to locate file paths.
• An external drive, network location, or cloud storage for the backup.
• For OST conversion (OST to PST), the Outlook account must be set up and synced.

Part 1: Backing Up Your Data

Step A: Identifying Your Data File Location

• Open Outlook.
• Go to File > Account Settings > Account Settings.
• Double-click your email account in the list.

- If you see a file path next to "Outlook data file," that is your PST file (POP/IMAP) or OST file (Exchange/Office 365).

- Alternatively, go to the Data Files tab in Account Settings to see all files and their paths.

• Note the file path (usually something like `C:\Users\YourUser\Documents\Outlook Files\...` or hidden in AppData).

Step B: Copying the File (Manual Backup)

• Close Outlook completely. (This is vital to unlock the file).
• Open File Explorer and navigate to the file path you identified.
• Copy the `.pst` or `.ost` file.
• Paste it into your secure backup location (e.g., External USB Drive).
• Rename the backup copy to include the date (e.g., `OutlookBackup-20260219.pst`).

- *Note: OST files are often large. Only back them up if you have a specific need or limited retention policies.*

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

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

• Open Outlook.
• Go to File > Open & Export > Import/Export.
• Select Export to a file > Next.
• Select Outlook Data File (.pst) > Next.
• Select the folder to export from (usually your account name at the top level to get everything).

- Check Include subfolders.

• Click Next.
• Choose a destination and filename.
• Click Finish.
• You may be asked to create a password for the backup file (optional).

Part 2: Restoring Data

Scenario 1: Outlook Can't Open Your Existing File

If your PST file is corrupt or Outlook won't start:

• Close Outlook.
• Locate the backup PST file you created.
• Copy the backup file to a safe location on your computer if it's currently on an external drive (Outlook files should run from internal storage or a reliable network share).
• Open Outlook.
• Go to File > Account Settings > Account Settings.
• Under the Data Files tab, select the broken data file and click Remove.
• Click Add... > Outlook Data File (.pst).
• Navigate to your backup file and select it.
• Set it as the default if desired.
• Restart Outlook. Your data should now be loading from the backup.

Scenario 2: Recovering Deleted Items or Old Emails

If you don't want to replace your whole data file but just want to retrieve specific old emails:

• Open Outlook.
• Go to File > Open & Export > Import/Export.
• Select Import from another program or file > Next.
• Select Outlook Data File (.pst) > Next.
• Browse to your backup file.

- Choose how to handle duplicates (e.g., "Replace duplicates with items imported from file").

• Click Next.
• Select the folder to import from (usually the top level of the backup file).
• Important: Select the destination folder (usually your current mailbox root or a subfolder like "Imported Backup" to avoid chaos).
• Click Finish.

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

If you deleted an Exchange/Office 365 account but have the OST file left:

• You cannot simply "Import" an OST file easily.
• You must convert it to PST first using a reliable third-party OST to PST converter tool (Microsoft does not provide a free built-in tool for this specific scenario).
• Once converted to PST, import it using Import from another program or file described in Scenario 2.

Best Practices for Data Files

• Regular Backups: Automate the backup of PST files using backup software or manual copying weekly.
• File Size Management: Keep PST files under 20GB if possible to reduce corruption risks. Use Outlook's AutoArchive feature (File > Info > Cleanup Tools > AutoArchive) to move old emails to a separate archive PST.
• Don't store on network drives: PST files should not be stored on network shares or roaming profiles as this causes corruption. OST files are server-caches and *can* be on local drives only.

Troubleshooting

• "The file cannot be opened": Ensure Outlook is fully closed (check Task Manager for `OUTLOOK.EXE`). Also, check file permissions.
• "Not a valid Outlook Data File": The file is likely corrupted. The automatic backup or the last backup is your only hope. Run SCANPST.EXE (referenced in KB-012) on the file.
• Prompt for Password: If you set a password on the PST during export, you must enter it to open it.

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 a specialized data recovery service or third-party software designed for Outlook repair.