Changes in Exchange Server 2013 public folder

Exchange supports moving your public folders 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

One of IT Admin's disappointments with Exchange 2010 is that PFs cannot be part of a Database Availability Group [DAG] and we still have to use the same replication method available for PFs to achieve resilience and high availability.

The good news is that with Exchange 2013 Preview, PFs do take advantage of the existing high availability and storage technologies of the mailbox store.PFs now being special mailboxes, there is no longer a Public Folder Database! The best part is that PF replication now uses the continuous replication model, and high availability for the PF mailboxes is achieved through a DAG, thus moving away from a Multi-Master Replication Model PFs had, to a Single-Master Replication Model of DAGs.

A Multi-Master Replication Model is one where you have two or more PF databases replicating between them. “Multi-Master” comes from the fact all PF databases are writable so you can have some users using one database, other users using the other database to access the same data, but their content is being constantly replicated between them, so all users have access to the same information. The problem is that this replication is done through SMTP messages sent between the servers holding the PF databases and is not very efficient, often causing conflicts when the same data is updated at the same time.

Because now PFs can be part of a DAG, we no longer have this multi-master replication model. Instead they replicate using the standard transaction log shipping method.

Changes in Exchange Server 2013

Exchange Server 2013 entirely changes how Public Folders operate

The main architectural changes that are introduced are:

*Public folders are now stored in a mailbox database

*Public folders now leverage a DAG for high-availability

Public Folder Mailboxes

Public folders are now also mailboxes, but their type is “Public Folder” (just like a Room Mailbox is a Mailbox with type “Room”). In a way, Public Folders still exist of two main elements mentioned above: the hierarchy and contents.

 * The hierarchy is represented by what is called the Master Hierarchy Public Folder Mailbox. This PF Mailbox contains a writable copy of your public folder hierarchy. There is only a single Master Hierarchy PF mailbox in the organization.

* Contents (in Public Folders) are now stored in one or more Public Folder mailboxes. These Public Folder mailboxes usually contain one or more Public Folders. Next to the contents, each PF Mailbox also contains a read-only copy of the hierarchy.

Note:-   because Public Folders are now stored in mailboxes, mailbox quota’s apply to them. For instance, this means that if a PF Mailbox would grow too large, you’d have to move Public Folders to another PF Mailbox (or increase the quota)