EDIT 3/31/2008: We have posted the updated public folder guidance for versions of Exchange past Exchange 2007; you might want to read it.

A frequent topic of discussion with customers is the future of Public Folders, thus I think it would be good to capture that discussion on our blog.

In summary:

1. Public Folders are widely used by our customers for sharing document, calendar, contact, and tasks; and for archiving distribution lists.
2. Exchange 12 (aka "E12") and Outlook 2007 (aka "Outlook 12") include public folder support - with great new investments in manageability and improved storage costs. Both of these products will be fully supported for 10 years from the availability of E12 - through at least 2016.  You can continue to use Public Folders with full support throughout this time.
3. Windows SharePoint Services is another option from Microsoft for, amongst other things: sharing document, calendar, contact, and tasks; and for archiving distribution lists. DL archiving and Outlook synchronization are new in Windows SharePoint Services v3 (WSS v3), which ships at the same time as Office 12 and E12.
4. For all new collaborative application development, we recommend WSS v3 and the new E12 web services as your platform, both of which are designed with .NET development in mind. We recommend maintaining existing Public Folder applications in-place.
5. All current versions of Outlook (from 97 through 2003) and Exchange (4.0 through 2003) require Public Folders to be deployed - Public Folders are required within an organization until all Outlook clients are upgraded to Outlook 2007, all mailboxes have been migrated to E12, and of course, no Public Folder applications are still used. Details below...

What are they?

Architecturally, Public Folders are a special mailbox, like all other mailboxes having a single top level folder hierarchy, but unlike all other mailboxes, Public Folders are stored in a dedicated database whose content can be replicated between servers. Administrators centrally manage this folder hierarchy, enabling end-users to create and modify folder content as they see fit.

What are they used for?

Public Folders were introduced in the first version of Exchange as a solution for sharing, discussion list archives, and as a platform for custom applications.

All current versions of Outlook (from 97 through 2003) also use Public Folders for four very important functions:

1)    Offline address book distribution

2)    Free/busy lookups

3)    Organizational form library

4)    Outlook Security settings

What did we introduce in Exchange 2003 SP2?

With Exchange 2003 SP2, we invested in the manageability of Public Folders.  A quick list of improved controls for administrators includes:

1)    stop and resume content replication

2)    apply delta changes recursively through a hierarchy

3)    synchronize the hierarchy

4)    ensure safe movement and/or removal of servers and stores

5)    log public folder deletions

Alongside SP2 we also shipped PFDavAdmin, which in addition to being a great tool for managing Public Folder permissions, addresses a very common customer request: how should you identify which public folders are stale (with the goal of deleting them/cleaning them up)? Unfortunately, virus scanning software accesses Public Folder content frequently, and current versions of Exchange do not have a good way to distinguish AV reads vs. end-user reads. We do however, have a clear understanding of when content was last modified. PFDavAdmin clearly identifies when Public Folder replicas and content has been last modified. If nothing has changed in 5 years, how interesting can it be?

What is new in 12?

As mentioned in the summary, Outlook 2007 and E12 will include support for Public Folders. Of course, there are some details worth noting:

1. E12's 64-bit storage optimizations accrue to Public Folders - providing a 70% reduction in IOPS requirements.
2. E12's MONAD command line experience can be used to manage E12 public folder deployments.
3. Outlook 2007 and E12 have greatly improved connection and synchronization logic, which accrues to both mailboxes and Public Folders.
4. E12 is the first version of Exchange that will enable customers to turn off Public Folders. When Public Folders are not available, Outlook 2007 is the only version of Outlook that supports:
   1. Offline address book distribution through a BITS http connection to the E12 client access server.
   2. Free/busy lookups through the new E12 availability web service
   3. Outlook Security settings from the registry deployed through Group Policy
   4. Organizational forms will be unavailable (Infopath forms are so much better, I recommend checking them out)
5. WSS v3 adds support for DL archiving and Outlook synchronization.
6. E12 OWA will support viewing documents shared through SharePoint sites.
7. E12's client access server has some limitations in public folder support: no IMAP, NNTP, nor OWA access to E12 public folders (OWA access to E2K and E2K3 public folders will be possible for E12 mailbox users).
8. E12 Public Folders continue to support replication across geographically distributed sites. WSS v3 has limited support for these topologies.

What is the plan for future versions of Exchange?

We are "de-emphasizing" Public Folders - which means that Public Folders may not be in our next major release after E12. That being said, let me re-affirm our commitment to fully support E12 Public Folders through at least 2016.

With this de-emphasis, we understand that some customers will be seeking prescriptive guidance on managing their Public Folder deployments. We will post more here soon. In the mean time, I recommend:

1. Plan on migrating to Outlook 2007 and Exchange 12.
2. Develop all new applications with .net
3. Watch this blog for detailed information on:
   1. IT data management (i.e. setting expiration limits on data, deleting unneeded data)
   2. End-user data management (to what extent can Outlook 2007 help end-users manage their Public Folder data)
   3. Partner solutions for data management

Thanks,

- Terry Myerson