How to Separate Merged PST Data in a Microsoft 365 Mailbox
Question details
The user needs to separate messages after accidentally importing one user's PST file into another user's Microsoft 365 mailbox.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Managing mailbox data after an accidental PST import synchronizes with Outlook on the web.
- Observed behavior
- The imported PST data merges with the existing mailbox data and the action cannot be automatically undone.
Ensure you create a complete backup of the current merged mailbox and have the original PST file available for reference before attempting any data separation.
Filter and Export Data Using the Original PST File
Use the original imported PST file as a reference to identify the incorrectly merged messages and move them out manually.
Because an accidental PST import cannot simply be undone once synced with Microsoft 365, you must manually isolate the incorrectly added items. By referencing the original PST, you can identify specific parameters to locate the merged data.
Access the mailbox where the PST was accidentally imported. Review the original PST file to determine specific dates, sender names, or unique folders associated with the imported data.
Use the Outlook search bar to filter emails based on the criteria you identified. Select the matching emails and move them to a newly created folder named 'Separated Data'.
Go to File > Open & Export > Import/Export. Choose 'Export to a file', select 'Outlook Data File (.pst)', and export the 'Separated Data' folder to a new, isolated PST file on your local drive.
Open the newly exported PST file in Outlook to ensure all data is intact. Once verified, you can safely delete the separated messages from the current user's mailbox.
Request Assistance from Microsoft Online Support
If the mailbox is business-critical or the merged data is too large to handle manually, Microsoft Support may offer backend assistance.
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Frequently Asked Questions
Can I click 'undo' after importing a PST file in Outlook?
No, once a PST file is imported and synchronized with Outlook on the web or Microsoft 365, the action cannot be directly undone with a simple click. You will need to manually separate the data.
Will Outlook rules help separate the merged mailbox?
Yes, you can create custom Outlook rules based on specific senders, recipients, or date ranges found in the original PST to automatically move these emails into a dedicated folder. However, you will still need to manually review the sorted items for accuracy.
Is it safe to delete the emails once I filter them out?
You should only delete the filtered emails after you have successfully exported them to a new PST file and verified that the original mailbox owner's data was not accidentally included in the batch.
Can I use the Import/Export wizard to remove the merged data?
The Import/Export wizard can only add data (import) or save data to a file (export). It does not feature a tool to 'remove imported data', meaning you must rely on manual filtering and exporting to isolate the merged files.
