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Public Folders: A Brief History

23 Mar 2017 by Laura Zawacki

For over 20 years Exchange public folders have been used as a space for collaboration, discussion, and even creating or tracking processes. Introduced in 1996 with Exchange 4.0, public folders were developed to provide similar, but improved, capabilities compared to services provided by Lotus Notes or IBM Domino’s. These services provided business collaboration functions, including email, calendars, to-do lists, contacts management, discussion forums, file sharing, IM and user directories.


What are public folders?

Put simply, public folders act as a repository for different information types. It enables users to organize content into a deep hierarchy, and all users will be able to see the full hierarchy in Outlook.

They were designed to:

  • Facilitate team collaboration.
  • Enable users to access data locally, and from remote locations or sites.
  • Offer self-management functionality, end users could create and use public folders with no administrators required.

With the release of Exchange 5.0, public folders also included newsgroup connectors, so that a newsgroup could be shared in public folders. Then in Exchange 5.5, an SMTP email address was included with each public folder – so they could send and receive mail.

They are supported in every Outlook/ OWA version, and creations and access permissions can be managed in Outlook by the end user. Once the public folder has been added to ‘favorites’, it can also be made available offline.


When to use public folders

There are several situations that merit the use of public folders. If a team needs a centralized location for emails, tasks, and calendars pertaining to a common project, department, or office site, then these folders are a good option. Public folders are an easy way to support large, global teams since they are accessible, discoverable and searchable for everybody with the necessary permissions. Using public folders also makes sense when Outlook usage is preferred because you can stay in one single application. Companies might also use them as central storage of shared calendars or contact lists. Long story short, it’s a great way to share information in Outlook without cluttering people’s inboxes.


Legacy Vs. Modern

Over the last few decades, public folders have evolved along with the Microsoft Exchange versions, however, they remained largely unchanged from their introduction in Exchange 4.0 to Exchange 2010.

These ‘legacy’ public folders are stored in dedicated public folder databases that cannot be moved between Exchange servers. These public folders can be replicated to multiple public folder databases, which results in faster access to content and reduces communication across WAN links between physical locations.

With the introduction of Exchange 2013, the public folder experience was modernized while maintaining the same end user experience that users were familiar with. In these ‘modern’ public folders, the databases where they were stored were replaced by mailboxes, which are stored in regular mailbox databases. Each mailbox includes the complete hierarchy (read only), which is based off the Primary public folder mailbox that contains the single writable copy of the hierarchy, and each public folder mailbox has unique content.


Issues with public folders

While public folders are a favorite among users, from an administrator perspective, there are some challenges. Legacy public folders are ungovernable; there is no way to track usage, content, or who is accessing which public folders. There is also no lifecycle management, so it’s likely that companies have stale folders and/or hierarchies that no longer apply to the current structure. Fortunately for users, Microsoft realizes that they are probably not going away anytime soon, and are addressing some of these challenges in Exchange on-premises, Exchange Online, and Office 365.


Exchange Online

In Exchange Online, public folder storage is available at no additional cost for up to 50 terabytes (1000 PF mailboxes with a 50 GB quota each). Once customers migrate their folders to Exchange Online, or create the first public folder mailbox, Microsoft will manage the storage.

There is also cross-premise access so Exchange Online users maintain access to on-premises public folders, and users of on-premises Exchange 2013 can access public folders within Exchange Online. Unlike the legacy on-premises public folders, Exchange Online public folders can be managed by the tenant admin through the Exchange Admin Center.


What’s New?

Several new features have been introduced, including full sync throttling, which limits the number of full syncs happening in parallel to 10, reducing the load on the Primary public folder Mailbox. Public folders also now have partial hierarchy that ensures that only the required parts of the hierarchy are copied to non-hierarchy serving mailboxes. This allows public folders to scale on the cloud.

Another new change is the addition of more supported topologies for Mac Clients. These users can now discover and access public folders in hybrid topologies, so Mac clients can maintain access to during a migration. These are just a few of the most recent enhancements, but there are many planned updates on the horizon.


What’s Next for public folders?

Microsoft is working to scale up public folders in Office 365 and on-premises. Today the max number of public folders in Office 365 is 100k folders, the max public folder mailbox count is 1000 mailboxes, and the max concurrent connections per mailbox is 2000 connections. Be on the lookout for continually increasing folder, mailbox and connection counts, especially in the cloud.

The feature roadmap also includes tools for usage reporting, policies for enabling/disabling public folders for users, introduction of Azure AD Connect for public folders, and support for public folder Office 365 migrations, and public folder to Groups migrations. In fact, this week Microsoft announced the availability of public folder migration from Exchange 2013/2016 on-premises to Exchange Online.

While the capabilities and limitations have evolved over the years, one thing remains steady – users love public folders because of their deep integration with Outlook and the practical way they enable information sharing. In our next part of this series, we’ll be looking at the types of content you can find in public folders.