Which Public Folders can Move to Exchange Online?
Microsoft documents batch migration of modern public folders from Exchange Server 2013 CU15 or later, Exchange Server 2016 CU4 or later and Exchange Server 2019.
Microsoft states in its legacy article that migrations from Exchange Server 2010 and older to Exchange Online are blocked starting October 1, 2025. Confirm the status with Microsoft before you plan a legacy move.
| Source | Path |
|---|---|
| Exchange 2013 CU15 or later | Batch migration to Exchange Online |
| Exchange 2016 CU4 or later | Batch migration to Exchange Online |
| Exchange 2019 | Batch migration to Exchange Online |
| Exchange 2010 and older | Blocked from October 1, 2025 per Microsoft |
What Limits should You Check First?
| Item | Limit or advice |
|---|---|
| Public folder mailboxes in Exchange Online during migration | Up to 100 |
| Size of one public folder mailbox | Up to 100 GB, fill to 50% |
| Total data advised for migration | 5 TB or less |
| One public folder without subfolders | 25 GB or less |
| Recoverable items quota per mailbox | 15 GB or less advised |
| Migration batches | One only |
The Microsoft prerequisites ask you to migrate users first, remove the backslash and forward slash from folder names and clear the Exchange Mail Public Folders option in Microsoft Entra Connect. Do not use Outlook PST export for hierarchies over 30 GB.
How does the Batch Migration Work?
Method #1: Native Batch Migration (Free)
Who it suits. Admins with a hybrid setup and PowerShell skills. Extra application. Exchange Management Shell and Exchange Online PowerShell.
- Download the Microsoft public folder migration scripts and prepare the source.
- Generate the folder to mailbox CSV file.
- Create the target public folder mailboxes in Exchange Online.
- Create the migration endpoint and the batch, then start it.
- Lock the folders on the source before the last sync.
- Finish the batch, test with a pilot user and unlock.
New-MigrationBatch -Name PublicFolderMigration -CSVData $bytes -SourceEndpoint $PfEndpoint.Identity
Start-MigrationBatch PublicFolderMigration
Complete-MigrationBatch PublicFolderMigrationMicrosoft advises at least 48 hours of downtime for the final sync. Public folders remain unavailable during that time, and no more data syncs after the batch reaches Completed.
What if the Native Path does Not Fit?
Method #2: Export to PST and Reimport (Free With Outlook)
Who it suits. Small hierarchies under 30 GB. Extra application. Outlook.
Export the folders to PST in Outlook and import them into the Exchange Online public folders. Microsoft advises against PST export for large hierarchies, because changes made during export are lost.
Mailbox moves use a different tool. The Exchange to Office 365 Migrator moves emails, contacts and calendars from Exchange 2010 to 2019. Its page does not list public folders, so check with the vendor before you rely on it for them.
What should You do After the Migration?
- Set a pilot user and test the hierarchy, permissions and posting.
- Compare folder counts with your baseline snapshot.
- Unlock the source only after the tests pass.
- Prepare a rollback plan for the first days.
Outlook problems with public folders are covered in our guide for Exchange 2013 public folders in Outlook 2016. Read the Exchange Online migration checklist for the wider plan.
Frequently Asked Questions
Which Versions can Migrate Public Folders to Exchange Online?
Microsoft lists Exchange 2013 CU15 or later, 2016 CU4 or later and 2019 for the modern path.
Can You Migrate Exchange 2010 Public Folders?
Microsoft states that migrations from Exchange 2010 and older to Exchange Online are blocked starting October 1, 2025.
How Much Downtime should You Plan?
Microsoft advises a minimum of 48 hours for the last sync.
What is the Size Limit for One Public Folder?
Microsoft advises 25 GB or less for one folder without subfolders.
How Many Migration Batches can You Create?
Only one. After the batch reaches Completed, no more data can sync.
Do Users Move Before Public Folders?
Yes. Microsoft advises that you migrate users to Microsoft 365 before you migrate public folders.
Can PST Export Move Public Folders?
Microsoft advises against it for hierarchies over 30 GB, because changes made during export are lost.
Author's Verdict
Check your version and folder sizes first, because the limits decide if the native path works.
Plan the 48 hour downtime window and test with a pilot user before you unlock.
Key Takeaways
- Modern public folders move by batch migration.
- Plan 48 hours of downtime.
- Exchange 2010 paths are blocked per Microsoft.
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