Limits for public folders

Summary: Learn about supported limits for public folders in Exchange 2016.

In Exchange 2016, public folders are based on a mailbox architecture that allows public folders to benefit from things such as the resiliency of a Database Availability Group (DAG) and other mailbox enhancements. However, there are limits and performance considerations that should be taken into account.

Limits

The following table lists the limits for public folders in on-premises Exchange 2016. Unless the limits are specifically stated as recommended, the values listed in this table are the supported limits for public folders.

Important

Looking for Exchange Online limits for Office 365? See Exchange Online Limits.

Item Limits Notes
Total number of public folder mailboxes
1,000
1,000 is the limit for Exchange Server 2016 CU2 or later. Although you can create more than 1,000 public folder mailboxes, it isn't supported. Create a public folder mailbox
Total public folders in hierarchy
1,000,000
Although you can create more than 1,000,000 public folders, it isn't supported. For any deployment of 100,000 or more public folders, we recommend reading Considerations when deploying public folders.
Sub-folders under the parent folder
10,000
While you can create more than 1,000 sub-folders under a parent folder, we don't recommend that you do so.
FolderHierarchyChildrenCountReceiveQuota parameter on the Set-Mailbox cmdlet.
Folder depth
300
The folder depth is the number levels of nested folders that can exist in one branch of a public folder tree. FolderHierarchyDepthRecieveQuota parameter on the Set-Mailbox cmdlet.
Maximum messages per public folder
1 million
MailboxMessagesPerFolderCountRecieveQuota parameter on the Set-Mailbox cmdlet.
Maximum individual public folder size
10 GB
This limit doesn't include subfolders beneath a single folder.
Configure storage quotas for a mailbox
Public folder mailbox size
100 GB
Configure storage quotas for a mailbox
Number of user logons per public folder mailbox
2,000 concurrent user logons
We recommend that you configure your hierarchy so that you have no more than 2,000 users per public folder mailbox. For example, if you have 20,000 users, you should have 10 public folder mailboxes.
Moved item retention
14 days recommended
Use the DefaultPublicFolderMovedItemRetention parameter on the Set-OrganizationConfig cmdlet.
Age limit
We recommend that you set this as the same default that you use for regular mailboxes.
These settings can be set at the following levels:
Organizational level: The DefaultPublicFolderAgeLimit parameter on the Set-OrganizationConfig cmdlet.
Mailbox level: The AgeLimit parameter on the Set-Mailbox cmdlet.
Folder level: The AgeLimit parameter on the Set-PublicFolder cmdlet.
Deleted item retention
We recommend that you set this as the same default that you use for regular mailboxes.
These settings can be set at the following levels:
Organizational level: The DefaultPublicFolderMovedItemRetention parameter on the Set-OrganizationConfig cmdlet.
Mailbox level: The RetainDeletedItemsFor on the Set-Mailbox cmdlet.
Folder level:: The RetainDeleteItemsFor parameter on the Set-PublicFolder cmdlet.
Maximum number of public folders that can be migrated to Exchange 2016
500,000
This is the maximum number of public folders you can move to Exchange 2016 from a legacy version of Exchange in a single migration. For details on migrating public folders, see Use batch migration to migrate public folders to Exchange 2016 from previous versions.