Email Migration

How to Automate Public Folder Migration from PST Files in Exchange Hybrid

Tauseeq Magsi Sep 25, 2026 868 views

Question details

The user needs a reliable method to migrate approximately 5 TB of public folder data from numerous PST files in a hybrid Exchange setup without manual copying.

Automate Public Folder Migration from PST Files

Product: Microsoft Exchange
Device & OS: not provided
Scenario: Migrating a massive 5 TB dataset from scattered PST files into public folders and shared mailboxes within a complex Exchange Hybrid environment.
Observed behavior: The current process relies on extensive manual copying, which is time-consuming and frequently results in duplicate folders due to the large item count.

Before you start

Ensure you have Microsoft 365 Global Administrator or Exchange Administrator privileges, and maintain a complete, secure backup of all on-premises PST files before attempting a bulk migration.

Solution 1Recommended

Open a Support Request in the Microsoft 365 Admin Center

For enterprise-level migrations exceeding several terabytes, Microsoft Support can provide backend assistance and specific automation tools to prevent folder duplication.

Migrating 5 TB of public folder data across hybrid environments is a highly complex scenario. Because standard manual imports via Outlook will likely time out or create duplicate trees, engaging Microsoft directly is the safest approach.

Access the Admin Center

Navigate to Support

Click on 'Support' in the left-hand navigation pane, then select 'Help & support' or 'New service request'.

Submit the Migration Request

Describe your 5 TB hybrid migration scenario in detail. Specify that you have multiple shared mailboxes, a high item count, and require automated ingestion methods to avoid duplicate public folders.

Open a Support Request in the Microsoft 365 Admin Center

Subscription Requirement: This option is available if you have an active Microsoft 365 Business or Enterprise subscription.

Solution 2

Consult the Exchange Hybrid Management Community

Leverage Microsoft's specialized engineering community to find custom PowerShell scripts and third-party recommendations tailored to high-volume PST migrations.

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Frequently Asked Questions

Why do duplicate folders appear when manually importing large PST files?

When manually copying large amounts of data, network interruptions or client timeouts can cause the import process to restart or lose track of previously synced items. In hybrid environments, synchronization delays between on-premises and cloud servers can also result in overlapping folder structures being created.

Is there a size limit for individual PST files during an Exchange migration?

While PST files can technically reach up to 50 GB, it is highly recommended to keep individual files under 20 GB before attempting a migration. Larger files are prone to corruption and dramatically increase the risk of connection timeouts during upload.

Can I use the Microsoft 365 Network Upload tool for public folder data?

The Network Upload tool (AzCopy) is primarily designed for importing PST files into standard user mailboxes and archive mailboxes. Migrating massive PST datasets directly into modern Public Folders often requires specific mapping scripts or specialized third-party migration tools to route the data accurately.

What is the best way to handle large shared mailboxes during a hybrid migration?

For large shared mailboxes, it is best to provision them directly in Exchange Online first, then use a staged migration batch or a specialized ingestion service to migrate the data incrementally. This avoids overwhelming the client application and minimizes duplicate item creation.