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Microsoft 365 Exchange Online Public Folder Size Limits and Migration
Question details
The user needs to know the size limits, auto-splitting capabilities, and supported migration methods for public folders in Microsoft 365 Exchange Online.
- Product
- Microsoft 365 Exchange Online
- Device & OS
- not provided
- Scenario
- Migrating a large on-premises public folder hierarchy to Microsoft 365.
- Observed behavior
- To ensure a successful migration, administrators must adhere to individual folder limits (15-25 GB) and mailbox limits (100 GB) while utilizing supported batch migration tools instead of Outlook PST exports.
Before planning your migration, review Microsoft's current official documentation as Exchange Online mailbox limits and supported PowerShell scripts are subject to periodic updates.
Plan and Execute Public Folder Migration Using PowerShell Batch Process
Use the official PowerShell batch migration method while adhering to mailbox size limits to ensure a smooth transition to Exchange Online.
Public folder migration requires careful mapping and size management. Individual public folders should generally be limited to 15-25 GB, while the maximum size of a public folder mailbox is typically 100 GB. Exchange Online utilizes an auto-split feature to expand storage when a public folder mailbox reaches its limit. Exporting via Outlook PST is highly discouraged for large environments.
Review your existing public folder hierarchy on the source server and remove any stale, unused, or oversized items.
Validate your existing folders to ensure individual sizes fall within the recommended 15 to 25 GB limit for better manageability.
Use Microsoft's provided PowerShell scripts to map your on-premises public folders to Exchange Online mailboxes accurately.
Select and create the target public folder mailboxes. Ensure these targets are not filled beyond approximately 50% of their total capacity during the initial migration.
Execute the PowerShell batch migration process from the Exchange Admin Center or PowerShell terminal instead of performing manual Outlook PST exports.
Looking for a Lightweight and Compatible Office Suite?
While planning your organization's server and email migrations, you might also be evaluating client-side office software. WPS Office provides a free, lightweight, and powerful alternative to Microsoft Office, offering an intuitive interface and seamless compatibility for your entire workforce.
- 1. Download the Installer: Visit the official WPS Office website and click on the 'Free Download' button for your operating system.
- 2. Install WPS Office: Run the downloaded setup file and follow the on-screen instructions to complete the lightweight installation.
- 3. Open and Edit Your Files: Launch WPS Office and seamlessly open your existing Microsoft Office documents without any formatting loss.
Frequently Asked Questions
What is the maximum size for an Exchange Online public folder mailbox?
The current maximum size of a public folder mailbox in Exchange Online is typically 100 GB. However, during an initial migration, you should not fill the target mailboxes beyond 50% capacity.
Can I migrate public folders using an Outlook PST export?
Exporting public folders through an Outlook PST file is strongly discouraged for large environments. You should use the officially supported PowerShell batch migration procedure for better reliability and performance.
How large should an individual public folder be?
To maintain optimal performance and manageability, individual public folders should generally be limited to approximately 15 to 25 GB before moving them to Microsoft 365.
What happens when a public folder mailbox reaches its size limit?
Exchange Online utilizes an auto-split feature. When a public folder mailbox approaches its size limit, the system automatically expands storage by splitting the data into a new public folder mailbox.
