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

Important Differentiations

• PST file: An Outlook Data File used primarily for POP and IMAP accounts, or for archiving data from Microsoft 365 accounts. It contains local copies of emails, contacts, and calendar items.
• OST file: An Offline Outlook Data File used by Microsoft 365 and Exchange accounts. It is a local cache of your server mailbox and is regenerated from the server. It generally does not need to be backed up as a primary strategy. If you lose access to 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 or local internal drive for the backup.
• For OST conversion, the Outlook account must be set up and synchronized. See How to add email to Outlook 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. Click the Data Files tab to view all data files and their paths.

1. Note the file path for the data file you wish to back up.

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 file.
4. Paste it into your secure backup location.
5. Rename the backup copy to include the date, for example OutlookBackup-20240520.pst.

Step C: Using Outlook’s Export Feature (Recommended for Microsoft 365)

For Microsoft 365 and Exchange accounts, use Outlook’s Export feature to create a PST backup of your mailbox data. Do not rely on manually copying OST files.

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.

1. Click Next.
2. Specify a destination and filename for the new PST.
3. 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).
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.

1. Click Next.
2. Select the folder within the backup you wish to import (usually the top-level mailbox).
3. Choose a destination folder in your current mailbox (e.g., a new folder called “Imported Backup”) to keep things organised.
4. Click Finish.

Scenario 3: Recovering Deleted Items from the Server (Microsoft 365)

For Microsoft 365 accounts, deleted items are often recoverable from the server even if they are not in your local backup.

• Check the Deleted Items folder first.
• If the item is not there, look in the Recoverable Items folder.
• For detailed steps on recovering deleted emails, see Deleted Email Recovery.

Scenario 4: Recovering Data from a Deleted Account (OST to PST)

If an Exchange or Microsoft 365 account has been removed but the local .ost file remains, note the following:

• Outlook cannot directly import an OST file.
• Do not re-create the account in Outlook expecting to recover deleted data from a local OST file. Re-creating the account generates a fresh OST synchronized from the server and will overwrite any local cache.
• If you must retain original data from a deleted account, use a reputable third-party OST-to-PST converter only as a last resort.

Scenario 5: Repairing a Corrupted PST File

If Outlook reports that your PST file is corrupted or cannot be opened, use the Inbox Repair Tool (scanpst.exe).

1. Close Outlook completely.
2. Locate scanpst.exe on your computer. Common locations include:
• C:\Program Files\Microsoft Office\root\Office16\ (Microsoft 365)
• C:\Program Files (x86)\Microsoft Office\Office16\ (Office 2016)
• C:\Program Files\Microsoft Office\Office15\ (Office 2013)
3. Double-click scanpst.exe to open the Microsoft Outlook Inbox Repair Tool.
4. Click Browse and select your corrupted .pst file.
5. Click Start to begin scanning.
6. If errors are found, click Repair to fix them.
7. Once complete, open Outlook and verify your data.

New Outlook (Web-Based)

New Outlook for Windows does not use local PST or OST files in the same way as classic Outlook. Data is stored primarily on Microsoft 365 servers. Users should rely on Microsoft 365 server-side retention policies, archive mailboxes, and eDiscovery tools for data protection rather than local PST backups.

Best Practices

• Schedule regular PST backups using Outlook’s Export feature, especially before major system changes or hardware upgrades.
• Store backup PST files on a local internal drive or dedicated external USB drive. Do not store them on OneDrive, Dropbox, network drives, or other cloud-synced locations.
• Close Outlook completely before copying PST files manually.
• Name backup files with the date (e.g., OutlookBackup-20240520.pst) to maintain version history.
• Do not set passwords on PST files unless absolutely necessary, as lost passwords cannot be recovered by Microsoft.
• Monitor PST file size. Older Outlook versions have a 20 GB limit; newer versions support 50 GB or larger but performance may degrade with very large files.
• For Microsoft 365 and Exchange accounts, rely on server-side retention and use Export to PST only for local archiving.
• If you use New Outlook, configure Microsoft 365 retention policies and archive mailboxes instead of local PST files.
• Test your backup restoration process periodically to ensure files are readable and complete.