Limits for public folders

In Exchange Server, 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 Server. 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.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 from Exchange 2010 to Exchange 2016 500,000 This is the maximum number of public folders you can move to Exchange from Exchange 2010 in a single migration. For details on migrating public folders, see Use batch migration to migrate public folders from Exchange 2010 to Exchange 2016.