Migrating Exchange public folders to SharePoint Online is one of the more technically demanding operations in a Microsoft 365 migration project. Public folders have been part of Exchange environments for decades. The data structures, permission models, and workflow dependencies that have built up around them do not translate cleanly into SharePoint’s document library model.
IT administrators who have migrated mailboxes to Exchange Online often expect Public Folder migration to be similar in complexity. In reality, it is usually more challenging and often requires a purpose-built solution such as the Public Folder Connector to simplify the transition.
This post covers the six most common challenges that IT teams encounter when migrating public folders to SharePoint Online, and what you need to do to address each one.
Challenge 1: The Nested Hierarchy Does Not Map Cleanly to SharePoint
Exchange public folders can have deeply nested hierarchies – folders within folders within folders, sometimes 8 or 10 levels deep. SharePoint Online does not support that same depth in its native folder or library structure, and the structural model is fundamentally different.
In Exchange, a public folder is a container that can hold other containers as well as items. In SharePoint, the closest analogy is a document library with nested folders – but SharePoint sites, subsites, and libraries have their own structural constraints that do not map one-to-one to public folder hierarchies.
The result, if not planned carefully, is a migration that produces a SharePoint structure that mirrors the Exchange hierarchy but does not work well as a SharePoint environment. Deep nested folders in SharePoint can hit URL length limitations. Documents buried 8 levels deep become difficult to surface through search. Navigation breaks down.
The fix: Before migration begins, audit the full public folder hierarchy and make a deliberate mapping decision. Some branches of the hierarchy may become a SharePoint site. Others may become document libraries. Others may become folders within a library. This mapping exercise cannot be skipped, and it cannot be done automatically – it requires input from the people who use the content.
Challenge 2: Permission Structures Break During Migration
Public folder permissions in Exchange are granular and often inconsistent. Different folders in the same hierarchy can have different permission sets. Some folders are accessible to all users. Others are restricted to specific security groups or individual users. Some permissions are inherited from parent folders. Others have been explicitly overridden at the item level.
This permission complexity does not migrate automatically. SharePoint uses a completely different permission model – permissions are inherited from the site level down to the list, library, and item level. Breaking inheritance, which is the SharePoint equivalent of an Exchange folder-level permission override, should be used sparingly because it creates administrative complexity.
A migration tool that does not explicitly handle permission preservation will either flatten permissions (giving everyone access to everything) or fail to migrate permissions at all, leaving all content with default SharePoint permissions.
The fix: Use a migration solution such as the Public Folder Connector that audits source permissions, maps Exchange permission roles to SharePoint permission levels, and preserves them during migration. Always run a post-migration permission validation before decommissioning the source Public Folders.
Challenge 3: Mail-Enabled Public Folders Require Special Handling
Not all public folders are simple document containers. Mail-enabled public folders (MEPFs) have associated email addresses and receive inbound email. They are used as shared inboxes, distribution list archives, and departmental communication hubs. Some organizations have dozens of them.
When you migrate a mail-enabled public folder to SharePoint Online, the folder’s ability to receive email does not automatically come with it. SharePoint Online does not have a native equivalent of a mail-enabled public folder. The mail routing needs to be handled separately – typically by either converting the MEPF to a shared mailbox, creating a distribution group, or using Microsoft 365 groups with an associated SharePoint site.
If mail routing is not addressed as part of the migration plan, email that was previously delivered to the public folder will stop arriving after the migration. Users who rely on that content stream will lose access to incoming messages without warning.
The fix: Identify all mail-enabled public folders before migration begins. Decide on the replacement mail routing strategy for each one. Implement the replacement before the source public folder is decommissioned, and test mail flow end-to-end before cutover.
See how the Public Folder Connector helps simplify the transition while preserving your Public Folder content in modern Microsoft 365 environments.
Challenge 4: Large Data Volumes Cause Throttling and Timeout Issues
Microsoft throttles migration operations to protect service performance. When you are migrating large volumes of public folder content – particularly hierarchies with millions of items or terabytes of data – you will encounter throttling. Migration jobs slow down, timeout, or fail partway through.
Native Microsoft migration tools handle throttling inconsistently. Some tools will retry automatically; others will simply stop and report success without migrating all the content. This is a particularly dangerous failure mode because the migration appears to have completed when it has not.
The fix: Use a migration solution such as the Public Folder Connector, designed for large-scale Public Folder migrations with built-in throttle management, automatic retry logic, and comprehensive migration reporting. Break large migrations into batches and validate each batch before proceeding. Schedule migrations during off-peak hours to reduce competition for Microsoft 365 API resources.
Challenge 5: Users Lose Access During Cutover
Public folder content is frequently in active use during a migration project. Users are reading, writing, and replying to content in the folders while the migration is running. A poorly managed cutover can leave users unable to access the content they need while the migration is in progress.
In an Exchange-to-Exchange migration, this is managed through incremental sync – the migration tool continuously synchronizes changes from the source to the destination, and the cutover window is kept short. The same principle applies to public folder migrations, but it requires a tool that supports incremental sync for public folder content, not just a one-time bulk move.
The fix: Use the Public Folder Connector with incremental sync capability to keep SharePoint Online or Shared Mailboxes synchronized while users continue working in the source Public Folders. Run the initial migration in the background while the source folders remain live. Complete the final sync close to the scheduled cutover window to minimize the delta. Communicate the cutover schedule to affected users in advance.
Challenge 6: No Pre-Migration Audit Means Surprises During Migration
Many public folder migrations encounter unexpected problems mid-project: folders that are larger than expected, permission structures that are more complex than assumed, mail-enabled folders that were not documented, or content that is subject to legal hold and cannot be moved.
These surprises are avoidable. A pre-migration audit of the source public folder environment – covering hierarchy depth, total size by folder, permission structures, mail-enabled folder status, and item counts – eliminates the unknown variables before migration begins.
Without an audit, the project plan is built on assumptions. With an audit, it is built on facts.
The fix: Run the Public Folder Analyzer against your source environment before writing your migration plan. Use the audit output to inform hierarchy mapping, resource planning, timeline estimates, and then use the Public Folder Connector to execute the migration with confidence.
ExchangeSavvy’s Public Folder Analyzer helps you understand your source environment before migration, while the Public Folder Connector simplifies moving Public Folder content to SharePoint Online and Shared Mailboxes with preserved permissions, folder hierarchy, and incremental synchronization. Explore the Public Folder Connector to prepare for the retirement of Exchange Web Services (EWS).
