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Public Folders in Exchange Online

Exchange Online

Applies to: Exchange Online

Topic Last Modified: 2014-02-24

Public folders are designed for shared access and provide an easy and effective way to collect, organize, and share information with other people in your workgroup or organization. Public folders help organize content in a deep hierarchy that’s easy to browse. Users will see the full hierarchy in Outlook, which makes it easy for them to browse for the content they’re interested in.

Public folders are available in the following Outlook clients: Outlook Web App for Exchange 2013, Outlook 2007, Outlook 2010, Outlook 2013, and Outlook for Mac.

Public folders can also be used as an archiving method for distribution groups. When you mail-enable a public folder and add it as a member of the distribution group, email sent to the group is automatically added to the public folder for later reference.

Public folders aren’t designed for the following purposes:

  • Data archiving. Users who have mailbox limits sometimes use public folders instead of mailboxes to archive data. This practice isn't recommended because it affects storage in public folders and undermines the goal of mailbox limits. Instead, we recommend that you use In-Place Archiving as your archiving solution.

  • Document sharing and collaboration. Public folders don't provide versioning or other document management features, such as controlled check-in and check-out functionality and automatic notifications of content changes. Instead, we recommend that you use SharePoint Online as your documentation sharing solution.

For more information about public folders and other collaboration methods in Exchange Online, see Collaboration in Exchange Online.

For more information about public folder quotas in Exchange Online, see the service description topics Sharing and Collaboration and Exchange Online Limits.

For a list of public folder management tasks, see Public Folder Procedures in Exchange Online.

For more information about the public folder limits, see Exchange Online Limits.

Looking for the Exchange Server 2013 version of this topic? See Public Folders.

Public folder architecture uses specially designed mailboxes to store both the public folder hierarchy and the content. The main architectural components of public folders are the public folder mailboxes.

There are two types of public folder mailboxes: the primary hierarchy mailbox and secondary hierarchy mailboxes. Both types of mailboxes can contain content:

  • Primary hierarchy mailbox   The primary hierarchy mailbox is the one writable copy of the public folder hierarchy. The public folder hierarchy is copied to all other public folder mailboxes, but these will be read-only copies.

  • Secondary hierarchy mailboxes   Secondary hierarchy mailboxes contain public folder content as well and a read-only copy of the public folder hierarchy.

There are two ways you can manage public folder mailboxes:

  • In the Exchange admin center (EAC), navigate to Public folders > Public folder mailboxes.

  • In the Exchange Management Shell, use the *-Mailbox set of cmdlets.

The public folder hierarchy contains the folders’ properties and organizational information, including tree structure. Each public folder mailbox contains a copy of the public folder hierarchy. There’s only one writeable copy of the hierarchy, which is in the primary public folder mailbox. For a specific folder, the hierarchy information is used to identify the following:

  • Permissions on the folder

  • The folder’s position in the public folder tree, including its parent and child folders

The hierarchy doesn’t store information about email addresses for mail-enabled public folders. Email addresses are stored in the directory.

The public folder hierarchy synchronization process uses Incremental Change Synchronization (ICS), which provides a mechanism to monitor and synchronize changes to an Exchange store hierarchy or content. The changes include creating, modifying, and deleting folders and messages. When users are connected to and using content mailboxes, synchronization occurs every 15 minutes. If no users are connected to content mailbox, synchronization will be triggered less often (every 24 hours).If a write operation such as a creating a folder is performed on the primary hierarchy, synchronization is triggered immediately (synchronously) to the content mailbox.

Because there’s only one writeable copy of the hierarchy, folder creation is proxied to the hierarchy mailbox by the content mailbox users are connected to.

For more information, see Update the Public Folder Hierarchy.

Public folder content can include email messages, posts, documents, and eForms. The content is stored in the public folder mailbox but isn’t replicated across multiple public folders mailboxes. All users access the same public folder mailbox for the same set of content. Although a full text search of public folder content is available, public folder content isn’t searchable across public folders and the content isn’t indexed by Exchange Search.

Although there are many advantages to using public folders in Exchange Online, there are some things to consider before implementing them in your organization:

  • Outlook Web App is supported, but with limitations. You can add and remove favorite public folders and perform item-level operations such as creating, editing, deleting posts, and replying to posts. However, you can’t create or delete public folders from Outlook Web App.

  • Although a full text search of public folder content is available, public folder content isn’t searchable across public folders and the content isn’t indexed by Exchange Search.

  • You must use Outlook 2007 or later to access public folders in Exchange Online.

  • Retention policies aren’t supported for public folder mailboxes.

Exchange supports moving your public folders to Exchange Online from the following legacy versions of Exchange Server:

  • Exchange Server 2010 SP3

  • Exchange Server 2007 SP3 RU10

You can’t migrate public folders directly from Exchange 2003. If you’re running Exchange 2003 in your organization, you must move all public folder databases and replicas to Exchange 2007 SP3 RU10 or later. No public folder replicas can remain on Exchange 2003.

We recommend that you don’t use Outlook’s PST export feature to migrate public folders to Exchange Online. Exchange online public folder mailbox growth is managed using an auto-split feature that splits the public folder mailbox when it exceeds size quotas. Auto-split can’t handle the sudden growth of public folder mailboxes when you use PST export to migrate your public folders and you may have to wait for up to two weeks for auto-split to move the data from the primary mailbox. We recommend that you use the cmdlet-based instructions in Migrate Legacy Public Folder to Exchange Online to migrate your public folders. However, if you’ve elected to do a PST migration and have run into an issue where the primary mailbox is full, you have two options for recovering the PST migration:

  1. Wait for the auto-split to move the data from the primary mailbox. This may take up to two weeks. However, all the public folders in a completely filled public folder mailbox won’t be able to receive new content until the auto-split completes.

  2. Create a Public Folder Mailbox and then use the New-PublicFolder cmdlet with the Mailbox parameter to create the remaining public folders in the secondary public folder mailbox. This example creates a new public folder named PF201 in the secondary public folder mailbox.

    New-PublicFolder -Name PF201 -Mailbox SecondaryPFMbx

For details about how to migrate public folders to Exchange Online, see Migrate Legacy Public Folders to Exchange Online.

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