Note: Some of the documentation referenced may not be fully available at the time of publishing of this post.

Exchange Server 2013 Cumulative Update 6 (CU6) was released today and provides several important updates for modern Public Folders. This blog post introduces you to the updates delivered in CU6 and discusses our on-going investments in public folders.

10x Increase in Public Folder Limits

CU6 delivers the first round of investments we have made to scale up the limits for Public Folders in Exchange Server 2013. CU6 raises the folder count limit to 100,000 folders. This is a 10x increase over the prior limit as defined in the Exchange Server 2013 limits for public folders. This enables you to migrate and deploy larger Public Folder hierarchies on premises with Exchange Server 2013. Customers can immediately take advantage of this new scale by deploying CU6.


In addition to the increased folder scale capabilities CU6 delivers improvements for concurrent access of Public Folders by reducing lock contention in store for hierarchy sync and content mailbox access.

As you scale the number of public folders in Exchange you might need to keep track of the number of folders that have been created. Exchange PowerShell provides an easy way to see the current public folder count in Exchange Server 2013. Using the Get-PublicFolder and Measure-Object cmdlets you can readily get a current count of your public folders created in Exchange 2013.

Get-PublicFolder –Recurse –ResultSize Unlimited | Measure-Object
Count    : 40051
Average  :
Sum      :
Maximum  :
Minimum  :
Property :

Mail-Enabled Public Folder Permission Changes

This is an important change for customers already using Public Folders in Exchange Server 2013. Prior to CU6 unauthorized senders were able to send messages to mail-enabled Public Folders which means external users could send email to mail-enabled Public Folders regardless of permissions. With CU6, administrators must grant Anonymous users Create Items permissions in the mail-enabled Public Folder to allow external users the ability to send email to the mail-enabled Public Folder. Refer to the CU6 release notes Public Folders section for guidance on updating your configuration.

Automatic Public Folder mailbox readiness management after migration

An additional change delivered in CU6 for Public Folders helps improve the administrator experience post migration. All PF mailboxes serve hierarchy by default in Exchange Server 2013. We have introduced new logic to check if the hierarchy is fully synced to a mailbox after migration. If it is, then the mailbox is automatically made available to serve public folder hierarchy connection else we wait for full sync to complete. This eases work for admin to manually manage readiness of a mailbox after migration completes. Admins can still turn hierarchy serving off and on (default = on) as they please. Refer to the Public Folder article for specific attributes to control hierarchy sync.

Public Folder Deployment Guidance

The increased scale capabilities for public folders in CU6 enables more advanced configurations to begin migrating to modern Public Folders. To meet the needs of these large scale migrations the team has created deployment guidance to assist customers migrating larger scale public folder hierarchies. This deployment guidance will become available in the next few weeks. We will update this post with a link once it is available.

What’s Next

This is the first round of public folder scale improvements we are working to deliver as we shared in the prior Exchange team blog post. Scale improvements are targeted to increase again in a future update. Scale improvements will remain our top priority for Public Folder updates. Other updates such as OWA support for calendar and contacts and Public Folder reporting tools are expected to follow after delivering further scale updates.

Brian Shiers
Technical Product Manager


Frequently asked questions

Q: Is there a limit for the number of sub-folders within a single public folder?
A: The recommended maximum number of sub-folders is 1000. This is the level that has been validated and is the same limit used in Exchange Online.

Q: Is there a limit for the folder depth of the hierarchy?
A: The recommended maximum depth of the hierarchy is 300 folder levels. This is the level that has been validated and is the same limit used in Exchange Online.

Q: Does the increase in folder count change the number of public folder mailboxes or quota for public folders?
A: The number of public folder mailboxes and the total public folder quota remain unchanged. These and other limits are documented in Public Folder Limits article.

Exchange Team Blog

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