Fix PST Import Fails After Microsoft 365 SAS URL Expires
Question details
The user needs a way to resume or recover a PST file network import to Microsoft 365 after the original SAS URL used for the upload expired.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Uploading large PST files to Microsoft 365 via network upload, resulting in the storage session or SAS URL timing out before completion.
- Observed behavior
- Rerunning the import generates a new SAS URL, but the Microsoft 365 verification process cannot detect or locate the PST files previously uploaded using the expired URL.
Ensure you have administrative privileges in the Microsoft 365 Compliance Center and a stable, high-speed internet connection to prevent future timeouts during large data uploads.
Import PST Files Using the Outlook Desktop Client
If the network upload method consistently fails due to SAS URL timeouts, using the local Outlook desktop client is a highly reliable alternative for importing PST data directly into a Microsoft 365 mailbox.
This method avoids the Microsoft 365 backend network upload limits and Azure storage timeouts. It is especially useful for users who only need to migrate a few mailboxes rather than performing a massive batch migration.
Launch the Outlook desktop application. Click on 'File' in the top-left corner, select 'Open & Export', and then click on 'Import/Export'.
In the Import and Export Wizard, choose 'Import from another program or file' and click 'Next'.
Select 'Outlook Data File (.pst)' as the file type. Click 'Browse' to find the PST file on your local drive, choose your preferred options for handling duplicates, and click 'Next'.
Select the Microsoft 365 mailbox where you want to import the data. Click 'Finish' to begin the import process. Ensure Outlook remains open until the synchronization is fully complete.
Perform a Test Batch and Contact Microsoft Support
Verify if the issue is strictly related to file size and network timeout by testing a small file, then consult Microsoft Support for assistance recovering the old SAS URL session.
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Frequently Asked Questions
Why does the Microsoft 365 SAS URL expire during a PST upload?
The SAS (Shared Access Signature) URL provides temporary, secure access to Microsoft's Azure storage network. If the upload process takes too long—often due to massive PST file sizes or slow network bandwidth—the token automatically expires for security reasons.
Can I reuse the expired SAS URL to continue my PST import?
Generally, you cannot reuse an expired SAS URL. The Microsoft 365 import service requires an active token. Once it expires, restarting the process generates a new URL, and files uploaded to the expired URL may not be automatically detected by the import job.
Is there a recommended file size limit for network uploading PST files to Microsoft 365?
While Microsoft supports importing large data sets, it is highly recommended to keep individual PST files under 20 GB. This minimizes the risk of network timeouts, corrupted uploads, and SAS URL expirations during the migration process.
