How to Fix Unknown Error when Importing PST into Office 365?

Microsoft Purview is a centralized suite of data governance, compliance, and risk management solutions that help organizations to manage, protect, and govern their data across Microsoft 365 services. It includes Import services that allow you to import PST files into Microsoft 365 mailboxes.

However, at times, you encounter an “Unknown Error” during the import process, while using the Network Upload or Drive Shipping method. This unexpected error can interrupt the import process. It can occur due to varied reasons, such as password-protected or corrupted PST file, incorrect SMTP address in the CSV mapping file, insufficient permissions, or others. In this guide, we will take a look at the causes of the Unknown Error and ways to fix it.

Understanding the Unknown Error

The “Unknown Error” indicates that the import job has failed but Microsoft 365 could not determine the exact cause of the failure. As a result, the PST items may not be imported into the destination mailbox.

This error can appear at various stages of the import process, such as uploading the PST files to Azure Storage, validating the import mapping (CSV) file, or importing mailbox data into Microsoft 365. Because Microsoft 365 cannot identify the exact cause, it displays a generic “Unknown Error” instead of a specific error code.

When you download the import log from the job history section for a failed PST import job, the import log entry appears as follows:

archive.pst,user@contoso.com,Failed,Unknown,0,0

The 0 items imported and 0 items skipped entries indicate that the import job stopped before your mailbox items could be processed.

Reasons for the Unknown Error when Importing PST into Office 365

The common reasons for this error include:

• Corrupted or oversized PST files
• Password-protected PST files
• Incorrect CSV mapping or invalid SMTP address
• Insufficient permissions
• Unsupported mailbox configurations
• Temporary service interruptions
• Network or connectivity problems

Methods to Resolve the Unknown Error when Importing PST into Office 365

Below, we have mentioned some effective methods to fix this error.

Method 1: Remove the PST Password

Password-protected or encrypted PST files cannot be imported into Office 365 without entering the correct password. So, make sure that the PST files are not password-protected. To check this, you can try to open the PST file in Outlook. If it prompts you to enter the password, the file is protected.

You can open the PST file in Outlook after entering the password and then export the mail items to a new unencrypted file using the Import/Export wizard.

Method 2: Repair PST File using SCANPST.EXE

A corrupted PST file will prevent Microsoft 365 from indexing or processing the data. You can repair your corrupted PST file by using ScanPST.exe and import the repaired file again into Office 365.  

You can find this tool at the following locations based on your Outlook version.

ScanPST.Exe Location by Outlook Version

Now, follow these steps to repair your PST file using ScanPST:

Note: Ensure that Outlook is closed.

• Go to the SCANPST.EXE on your computer.

• Launch the utility by double-clicking it.

• Click Browse to select the affected PST file. Click Start.
• The tool will start scanning the file. If errors are found, click Repair.

Note: Run the tool again until no errors are reported.

Once the file is repaired, upload it to Azure Storage and restart the import job.

Method 3: Verify the CSV Mapping File

If the Mailbox column in the CSV mapping file contains an incorrect value, such as a display name instead of the user’s primary SMTP address, Microsoft Purview Import service cannot map the PST file to the correct mailbox. As a result, the import job may fail with an unknown error. Make sure the Mailbox column contains the user’s primary SMTP address, not the display name, alias, or UPN. Also, verify that all required columns are present in the CSV file.

You can verify the primary SMTP address by running the following command in Exchange Online PowerShell:

Get-Mailbox -Identity "Display Name" | Select PrimarySmtpAddress

Use the returned SMTP address in the Mailbox column.

Workload,FilePath,Name,Mailbox,IsArchive,TargetRootFolder Exchange,,archive.pst,user@contoso.com,FALSE/

Key Rules for Creating the PST Import CSV Mapping File

• Mailbox must contain the user’s primary SMTP address.
• Do not use the display name, alias, or UPN.
• TargetRootFolder must be / and should not be left blank.
• IsArchive must be FALSE when importing into the primary mailbox.
• Verify that the CSV mapping file is accurate before starting a PST import.

Method 4: Assign the Required Roles

Missing permissions can prevent Microsoft Purview Import Service from validating and processing the PST import job, which may result in an unknown error. Before starting the import, make sure your administrator account has the following roles:

• Mailbox Import Export role in Exchange Online.
• Must be a member of the Organization Management or another role group that includes the Mailbox Import Export role.

Method 5: Generate a New SAS URL

A SAS – Shared Access Signature – URL expires after seven days. If you start uploading PST files after the URL has expired, the import job may fail with an unknown error. In such a situation, you need to create a new import job in Microsoft Purview to obtain a fresh SAS URL.

To generate a new SAS URL:

• Open Microsoft Purview.
• Delete the old import job.
• Create a new import job.
• Copy the new SAS URL.

An Alternative Solution – Use Stellar Migrator for Outlook

If you are still facing issues or find the Microsoft Purview import process too complex, it is recommended not to invest more resources or time in troubleshooting. Instead, you can go for a specialized PST to Office 365 migration tool, such as Stellar Migrator for Outlook. This tool allows you to import Outlook PST files directly into Microsoft 365 mailboxes easily. You don’t need to configure Azure Storage, use AzCopy tool, or generate SAS URL. This makes the PST migration process simpler, faster, and easier to manage, especially for large-scale mailbox migrations.

Key features of this tool include:

• Imports multiple PST files into Microsoft 365 directly.
• Supports bulk migration using CSV mapping file.
• Migrates data to user and shared mailboxes.
• Preserves the original folder hierarchy.
• Filters mailbox items by date for selective migration.
• Automatically maps source PST files to target mailboxes.
• Supports password-protected and encrypted PST files.
• Provides advanced filtering options for controlled migration.

See our guide on How to Migrate PST file to Office 365 for more details.

Conclusion

In this guide, we have mentioned the causes of the “Unknown” error that occurs when importing PST into M365 and their fixes to solve this error. You can apply the right fix and complete the import process successfully. The manual troubleshooting process is too time-consuming and complex, you can use Stellar Migrator for Outlook to import PST files directly into Microsoft 365 or live Exchange Server mailboxes. This tool provides a simpler way to import PST files directly into Microsoft 365 mailboxes without using AzCopy or managing SAS URLs.  

FAQ