Email Migration

Fix Exchange Online PST Import and AzCopy Errors for Large Files

Tauseeq Magsi Oct 22, 2026 869 views

Question details

A large 30 GB PST file fails to import into Exchange Online using AzCopy or Outlook, with Outlook incorrectly reporting insufficient space.

Fix Exchange Online PST Import and AzCopy Errors for Large Files

Product: Exchange Online
Device & OS: not provided
Scenario: Migrating a 30 GB PST file to Exchange Online using AzCopy network ingestion or the Outlook desktop client.
Observed behavior: AzCopy fails during the Microsoft 365 ingestion process, and importing directly through Outlook fails with an 'insufficient OneDrive space' error despite having ample storage available.

Before you start

Ensure your local hard drive has enough free disk space to accommodate the entire 30 GB PST file locally, and verify that you are running the latest version of the AzCopy tool.

Solution 1Recommended

Fix Outlook Import by Downloading the PST Locally

Resolve the 'insufficient OneDrive space' error by moving the PST file out of cloud-synced folders before initiating the import.

Outlook often struggles to import large PST files directly from cloud-synced directories like OneDrive. The system may misinterpret cloud storage limits or encounter file-locking conflicts, leading to false 'insufficient space' errors.

Locate the PST in OneDrive

Open File Explorer and navigate to your OneDrive folder where the 30 GB PST file is currently stored.

Move to a Local Directory

Copy the PST file and paste it into a strictly local folder, such as your Desktop or a dedicated folder on your C: drive. Ensure the file status does not show a cloud icon (meaning it is not 'online-only').

Import through Outlook

Open Outlook, click on 'File', select 'Open & Export', and choose 'Import/Export'. Select 'Import from another program or file' and point it to the local copy of your PST file to complete the migration.

Fix Outlook Import by Downloading the PST Locally

Verification Complete: Importing from a local directory bypasses OneDrive sync conflicts and allows Outlook to process the large file smoothly.

Solution 2

Troubleshoot Microsoft 365 Network Ingestion (AzCopy)

Verify parameters, permissions, and size limits when using AzCopy to upload PST files to Azure Storage.

Solution 3

Create a Service Request with Microsoft Support

Escalate persistent Exchange or OneDrive environment issues directly to Microsoft business support.

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Seamlessly open, edit, and save Microsoft Word, Excel, and PowerPoint files (.docx, .xlsx, .pptx).Lightweight installation saves local disk space, helping prevent 'insufficient storage' issues.Free to use with a familiar tabbed interface, making migration effortless.

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Frequently Asked Questions

Why does Outlook say I have insufficient OneDrive space when importing a PST?

Outlook struggles to calculate space and manage file locks for large PST files stored in cloud-synced folders. It often misreads the available storage. Downloading the PST completely to a local, non-synced folder before importing usually resolves this.

What is the maximum recommended PST file size for Exchange Online network ingestion?

Microsoft strongly recommends keeping individual PST files under 20 GB. Files larger than this, such as a 30 GB PST, have a significantly higher chance of failing during the AzCopy upload or the mailbox mapping phase.

How do I ensure my PST file is not marked as 'online-only' in OneDrive?

Right-click the PST file in your OneDrive folder and select 'Always keep on this device'. Wait for the cloud icon next to the file to change to a solid green checkmark, indicating the file is fully downloaded to your local drive.

Migration & Recovery