Exchange Server 2016 Public Folders coexistence

If we are migrating from Exchange 2010 to Exchange 2016 and we are using Public Folders (PF), we need to set up public folder coexistence before moving the first mailboxes. Otherwise the folders will not be available to the migrated users.

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This article is part of a series based on my notes during the migration of an Exchange organization from version 2010 to 2016. It is not a complete procedure, but a description of the main points and areas. The examples relate to a specific design, but can generally be generalized. Similarly, although it is a description of a migration, the information is also suitable for a new installation or administration.

Official documentation: Exchange Server 2016, Public folders, Configure legacy public folders where user mailboxes are on Exchange 2013 servers, Configure legacy on-premises public folders for a hybrid deployment.

We will discuss public folders in more detail later, when we address their migration. For now, the important information is that the original (Legacy) Public Folders, which used a special database (Public Folder Database, which functioned differently than the Mailbox DB), were replaced by new ones (instead of being discontinued, as Microsoft had long promised) in Exchange 2013, often referred to as Modern Public Folders. These are stored in special mailboxes within the standard Mailbox Database.

This brings some advantages, such as the ability to use DAG (Database Availability Group). But also a different approach to public folders, which is important during migration. A user who has a mailbox on Exchange 2010 can only connect to Legacy Public Folders. If we set up coexistence, a user with a mailbox on Exchange 2016 can connect to both Legacy Public Folders (works only from Outlook, not OWA) and Modern Public Folders. It is worth noting that only one type of public folders can be active in the organization (so the original ones are used, then we perform the migration and switch to the new ones). It is probably unnecessary to note that on Exchange 2010 we can only operate Legacy Public Folders and on Exchange 2016 only Modern Public Folders.

From this follows the necessary order of steps if we want to maintain the functionality of public folders during the Exchange migration.

setting up coexistence
gradual mailbox migration
public folder migration (a one-time action)

Setting up coexistence - access to Legacy Public Folders

Official information Configure legacy public folders where user mailboxes are on Exchange 2013 servers.

This involves creating a special Proxy mailbox (in a separate DB on Exchange 2010) through which users from Exchange 2016 will access the public folders on Exchange 2010. And a global Public Folders setting to Remote.

Creating a proxy mailbox - setting up Exchange 2010 PF discoverable

We need to meet some prerequisites (which I consider standard). Installed CAS role on the servers where the PF DB is located, and Outlook Anywhere enabled.

Creating an empty Mailbox Database

We create a new mailbox database on one of the servers where the public folder databases are located. If we have some PF DBs only on another server (and there is no replica here), we need to create another new Mailbox DB there as well (if the folders are to be available).

Example of creating a DB using the Exchange Management Shell. It is recommended to create only a single mailbox in this DB, a Proxy Mailbox.

New-MailboxDatabase -Server MAILOLD -Name DBPFProxy -IsExcludedFromProvisioning $true -LogFolderPath E:\DBPFProxy -EdbFilePath D:\DBPFProxy\DBPFProxy.edb 
Mount-Database DBPFProxy

Creating a Proxy mailbox

In the new database, we create a standard mailbox and hide it from the directory. The SMTP address of this mailbox will be returned in AutoDiscover as DefaultPublicFolderMailbox. Clients will access Legacy Public Folders through it.

New-Mailbox -Name PFProxyMBX -Database DBPFProxy -UserPrincipalName PFProxyMBX@firma.local
Set-Mailbox -Identity PFProxyMBX -HiddenFromAddressListsEnabled $true

Configuring AutoDiscover to return the Proxy mailbox

Set-MailboxDatabase DBPFProxy -RPCClientAccessServer MAILOLD

Configuring user mailboxes for access to Legacy Public Folders

On Exchange 2016, we set the organization parameter to use remote public folders. In the command, we use all the created Proxy mailboxes if we created multiple databases.

Set-OrganizationConfig -PublicFoldersEnabled Remote -RemotePublicFolderMailboxes PFProxyMBX

For the overall application, AD DS replication must take place. Subsequently, we can view the account on Exchange 2016 and see the configured Proxy mailbox.

[PS] C:\>Get-Mailbox bouska | FL DefaultPublicFolderMailbox, EffectivePublicFolderMailbox

DefaultPublicFolderMailbox   :
EffectivePublicFolderMailbox : firma.local/Users/PFProxyMBX

Problems with access to public folders

I had some problems with access to the moved users' old PF. It turned out to be a matter of not properly following the procedure above (and I did not perform the procedures in the articles). But I came across information that I will just mention here. It is stated that the mailbox DB where the user's mailbox (who is connecting to PF) is located must have the same PF DB assigned to it as is assigned to the newly created database where the PF Proxy Mailbox is.

We can easily list which PF DB is assigned to individual servers.

[PS] C:\>Get-MailboxDatabase | FT ID, Server, PublicFolderDatabase

Id        Server     PublicFolderDatabase
--        ------     --------------------
DBPFProxy MAILOLD    DBPF

Related articles:

I was migrating an organization from Exchange Server 2010 to Exchange Server 2016. The whole process was quite demanding and long (it took me 4 months even with my studies). In the process, I came across a number of problems, errors and shortcomings (even in the official documentation). I am creating this series from my notes. This is not a complete guide to the transition, but highlights and mentions of issues I encountered. Individual articles describe different areas of Exchange Server 2016, so it is not only a transition from an older version, but also suitable for a new installation or administration.

Almost since the beginning of my practice, I have been involved in the administration of the Microsoft mail server, i.e. Exchange Server. I started with the 2003 version and worked my way up to Exchange Online. The articles cover many areas of management. Most since the migration to Exchange Server 2016 and its complete configuration. But also Exchange Hybrid and e-mail security.