Limits for public folders in Exchange Server
In Exchange Server, public folders are based on a mailbox architecture that benefits from the resiliency of a Database Availability Group (DAG) and other mailbox enhancements. However, there are limits and performance considerations that you should take into account.
Limits
The following table lists the limits for public folders in on-premises Exchange Server. Unless the limits are stated as recommended, the values listed in this table are the supported limits for public folders.
Important
Looking for Exchange Online limits for Microsoft 365 or 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 officially supported. See 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 officially supported. For any deployment of 100,000 or more public folders, we recommend reading Considerations when deploying public folders. |
| Subfolders under the parent folder | 10,000 | Although you can create more than 1,000 subfolders under a parent folder, it isn't recommended. The limit can be enforced with the 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. The limit can be enforced with the FolderHierarchyDepthReceiveQuota parameter on the Set-Mailbox cmdlet. |
| Maximum messages per public folder | 1 million | The limit can be enforced with the MailboxMessagesPerFolderCountRecieveQuota parameter on the Set-Mailbox cmdlet. |
| Maximum individual public folder size | 10 GB | This limit doesn't include subfolders beneath a single folder. See Configure storage quotas for a mailbox. |
| Public folder mailbox size | 100 GB | Although public folder mailbox size can exceed 100 GB, it isn't officially supported. See 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've 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: Use the DefaultPublicFolderAgeLimit parameter on the Set-OrganizationConfig cmdlet. Folder level: Use 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: Use the DefaultPublicFolderMovedItemRetention parameter on the Set-OrganizationConfig cmdlet. Mailbox level: Use the RetainDeletedItemsFor on the Set-Mailbox cmdlet. Folder level: Use 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. Although you can attempt to migrate more than 500,000 folders, it isn't officially supported. For details on migrating public folders, see Use batch migration to migrate public folders from Exchange 2010 to Exchange 2016. |