Office 365 Shared Mailbox to Public Folder Migration
An Office 365 shared mailbox and an Exchange Online public folder are different collaboration models. A shared mailbox provides a common mailbox and email address for a group of users, while public folders organize shared content in a folder hierarchy with folder-level permissions. A migration from a Shared mailbox to a Public folder should therefore be planned as a workload conversion, not as a generic tenant migration.
This page focuses specifically on Shared Mailbox → Public Folder. For broader mailbox migration capabilities, see the Office 365 migration Tool.
When Should You Move a Shared Mailbox to a Public Folder?
A Public folder can be appropriate when the organization needs a shared, hierarchical folder structure for content that multiple users must browse and access through Exchange/Outlook permissions. It can be useful for department-, project-, or topic-based organization and for business processes that already depend on public folders or mail-enabled public folders.
Public folders are not automatically the best destination for every Shared mailbox. If the primary requirement is long-term mailbox archiving, document collaboration, or modern team collaboration, another Microsoft 365 workload may be more appropriate.
Shared Mailbox vs Public Folder
| Feature | Shared mailbox | Public folder |
|---|---|---|
| Primary purpose | Shared mailbox access and common email address | Shared, organized folder-based content |
| Structure | Mailbox folders | Public folder hierarchy |
| Access model | Mailbox permissions such as Full Access, Send As, and Send on Behalf | Folder-level public-folder permissions |
| Email address | Can have its own SMTP address | A public folder can be mail-enabled when required |
| Calendar | Shared mailbox calendar | Calendar-type public folders can be used where supported |
| Storage architecture | Mailbox | Content stored in public folder mailboxes |
| Administration | Mailbox settings and permissions | Public folder hierarchy, permissions, mail enabling, and quotas |
Is a Public Folder the Right Destination?
| Requirement | Possible destination |
|---|---|
| Shared email address and ongoing team mailbox | Shared mailbox |
| Hierarchical shared Exchange folders | Public folders |
| Long-term mailbox archiving | Archive mailbox |
| Document sharing, versioning, and document collaboration | SharePoint |
| Modern team collaboration | Microsoft 365 Groups / Teams |
Microsoft does not recommend public folders as a general mailbox-archiving solution, and it recommends SharePoint for document-management scenarios that require features such as versioning. Choose the target according to the actual collaboration requirement.
Public Folder Prerequisites
Prepare the Exchange Online public-folder environment before connecting the migration tool. A public folder mailbox must exist before public folders can be created.
- Confirm that Exchange Online public folders are available in the target tenant.
- Create or verify the required public folder mailbox.
- Create the root public folder and the required subfolder hierarchy.
- Confirm administrator access and public-folder management permissions.
- Review the permissions required for users who will access the target folders.
- Check folder and public-folder-mailbox quotas before moving large Shared mailbox datasets.
- If a target public folder must receive email, configure and validate mail-enabled public folder settings separately.
Public Folder Storage Planning
Exchange Online public folders have defined capacity limits and should not be described as unlimited storage. Microsoft documents a 100 GB limit per public folder mailbox and support for up to 1,000 public folder mailboxes. Microsoft also recommends keeping an individual public folder under 10 GB because larger folders can create problems during the auto-split process.
Before migration, compare the Shared mailbox data volume with the planned target hierarchy. Large datasets may need to be distributed across an appropriate public-folder structure rather than placed into one oversized folder.
Shared Mailbox to Public Folder Migration Planning
- Inventory the source Shared mailboxes, including address, approximate size, folder structure, and item count.
- Identify users with Full Access, Send As, or Send on Behalf permissions so access requirements can be redesigned for public folders.
- Decide which source folders and date ranges are in scope.
- Prepare the target public-folder mailbox and hierarchy before mapping.
- Confirm target quotas, permissions, and any mail-enabled public-folder requirements.
- Review Microsoft 365 throttling, message-size limits, network capacity, and expected migration volume.
- Test a representative Shared mailbox before a large migration.
- Define post-migration validation criteria and keep the source available until the result is validated.
Permissions and Access Mapping
Shared mailbox permissions and public-folder permissions are different permission models. Source permissions such as Full Access, Send As, and Send on Behalf should not be assumed to become equivalent public-folder permissions automatically.
Review and recreate the required target folder permissions according to the new hierarchy. Validate owner, publishing, reviewer, read, write, and mail-enabled public-folder access as applicable to the organization.
Supported Data and Migration Scope
The existing EdbMails workflow on this page demonstrates migration from source Primary/Shared Mailboxes to target Public Folders. Treat the migration scope as supported mailbox content selected by the current product workflow.
Do not assume that every mailbox item type or every source mailbox property has a one-to-one representation in a public folder. Review the selected folders/items, migration options, and final report, then validate representative messages, attachments, folder structure, and supported item properties at the target.
Prepare and Verify the Source-to-Public-Folder Mapping
The target public-folder hierarchy should be prepared before mapping. For example, a Support Shared mailbox may map to \Support, HR to \HR, and Sales to \Sales.
In EdbMails, review each source Shared mailbox and source folder against the intended target public folder. Where automatic mapping is available, verify it before migration. Use manual mapping when the source content must be directed to a specific target folder.
Migrate an Office 365 Shared Mailbox to a Public Folder with EdbMails
Step 1: Download and install EdbMails Office 365 migration software
- Download and install the EdbMails application on your computer running on Windows OS.
- Start the application and enter the required details and click the ‘Login’ button or click the ‘Start Your Free Trial’ button to continue.
- Select the ‘Office 365 Migration’ option
- Select the ‘Office 365 to Office 365 Migration’ option
- Keep the default job name or click the ‘New Job’ button to change it.
Step 2: Connect to source Office 365 server
- Click the ‘Add New Connection’ button to create a new connection to the source Office 365, or select a previous connection from the list and click ‘Connect to Existing’ to proceed.
- Select the ‘Connect to Primary/Shared Mailboxes’ option.
- Click the ‘Next’ button to proceed.
- Select a secure OAuth 2.0-based modern authentication method and click the ‘Login’ button to continue.
Connect to Office 365 server using secure modern authentication
- Authenticate on Microsoft sign-in page.
- After successfully connecting to your Office 365 server, select an option to load the mailboxes. Alternatively, you can also load the mailboxes using a CSV file.
- Click the ‘Add New Connection’ button to create a new connection to the source Office 365, or select a previous connection from the list and click ‘Connect to Existing’ to proceed.
Step 3: Select Office 365 Shared mailboxes
- Select the Shared mailboxes from the left pane
- Click ‘Next’ to continue
Step 4: Connect to target Office 365 server
- Click the ‘Add New Connection’ button to create a new connection to the target Office 365.
- To use a previous connection, select it from the list and click ‘Connect to Existing’ to proceed.
- Select ‘Connect to Public Folder’ as your connection method, then click ‘Next.’
- Select your preferred authentication method and click the ‘Login’ button to continue.
- Sign in on the Microsoft login page.
- Choose a method to load the mailboxes and click the 'Next' button to continue.
Step 5: Map Shared mailboxes to public folders
- Use the EdbMails mapping screen to review how each source Shared mailbox and its folders are mapped to the prepared target public-folder hierarchy. Where automatic mapping is available, verify the result before starting migration; otherwise, select the required target public folder manually.
- Use the EdbMails mapping screen to review how each source Shared mailbox and its folders are mapped to the prepared target public-folder hierarchy. Where automatic mapping is available, verify the result before starting migration; otherwise, select the required target public folder manually.
Step 6: Start Office 365 Shared mailbox to public folder migration
- Once the mailboxes are mapped, click the ‘Start Migration’ button to initiate the migration process.
- After the migration starts, use the ‘View Log’ button to review the migration report. Check completed, skipped, failed, and unmapped items, then validate representative content in the target public folders.
- Once the mailboxes are mapped, click the ‘Start Migration’ button to initiate the migration process.
Incremental Migration, Filters, and Throttling
EdbMails supports incremental migration for subsequent runs so newly added or changed items can be processed according to the migration configuration rather than repeating the entire initial data set.
Where supported by the current workflow, use migration filters such as date range and source-folder selection to limit the migration to the required data.
EdbMails can adjust migration activity when Microsoft 365 throttling occurs. Migration speed can still vary based on Microsoft service limits, source data volume, item count, network conditions, and the selected concurrency.
Post-Migration Validation
- Compare representative messages and attachments with the source Shared mailbox.
- Verify the target public-folder hierarchy and the expected folder locations.
- Review the migration report for completed, skipped, failed, or unmapped items.
- Confirm that the required users can open the target public folders and have the intended read/post permissions.
- If a public folder is mail-enabled, send a test message and confirm delivery and address behavior.
- Test access from the Outlook clients actually used by the organization.
MX-record changes, Autodiscover changes, and new Outlook profiles are not standard steps for a Shared Mailbox → Public Folder migration. If this workload is part of a larger tenant/domain migration, handle those cutover tasks separately.
Public Folder Client Access
Public-folder access depends on the Outlook client and feature being used. Microsoft documents public-folder access in Outlook for Windows, Outlook for Mac, and Outlook on the web, with client-specific limitations. Do not position public folders as inherently providing better mobile access than Shared mailboxes.
Common Shared Mailbox to Public Folder Migration Problems
- Target public folder is not available: Verify that a public folder mailbox and the required folder hierarchy exist and that the connecting administrator has access.
- Mapping is incorrect: Review the source Shared mailbox/folder and target public-folder path and correct the mapping before starting migration.
- Permission behavior differs after migration: Recreate the required public-folder permissions; Shared mailbox permissions do not directly translate to public-folder permissions.
- Some content is missing: Review migration scope, filters, source permissions, target quotas, and the migration report.
- Migration is slower than expected: Review Microsoft 365 throttling, public-folder capacity, source data volume, item count, network conditions, and concurrency.
For additional troubleshooting, use the existing Office 365 migration troubleshooting guide and Public folder troubleshooting.
Related Migration and Alternative Scenarios
If the requirement changes from Shared Mailbox → Public Folder, use the workload-specific guide rather than broadening this page:
- For archive mailbox migration to Exchange Server, see the office 365 archive mailbox to exchange guide.
- For public folders moving between Microsoft 365 environments, see the office 365 public folder migration to office 365 guide.
- For public folders moving to Exchange Server, see the office 365 public folder to exchange guide.
- If a PST-based export is the intended outcome instead, see the office 365 migration to pst guide.
