Configure Hybrid Public Folder with Exchange 2013/2016 (aka Modern Public Folders)

Public Folders don’t seem to have the usage that they used to so it’s been a while since we worked with Public Folders in Exchange. So long in fact that what we last configured is now called Legacy Public Folders with the new version, introduced in Exchange 2013 called Modern Public Folders.

A Refresher on Exchange Public Folders

In order to understand the new process of setting up Hybrid mode with Exchange Online you first need to understand some changes to how Public Folders work.

In Exchange 2010 public folders were stored in dedicated Public Folder Databases. These also had their own log files and had to be managed independently of any User Mailbox Databases.

With Modern Public Folders they have been moved into Mailboxes which are stored in a standard user database. The environment can contain multiple public folder mailboxes, each of which can contain different parts of the public folder hierarchy.

When a user accesses a public folder they are actually opening the mailbox that contains that part of the hierarchy. Unlike previous versions the data is only accessible from the server hosting the active database rather than any server hosting a public folder replica.

Configuring Hybrid Public Folders

What does this mean for configuring Hybrid mode Public Folders?

First of all if you searched for something like “Configure Exchange Public Folder Hybrid” and found this Exchange 2019 article referring to Exchange 2010 SP3 or later then you’ve got the wrong article. You need to look for this article which is only on the Exchange Online documents site.

This newer article ignores all of the steps setting up new Public Folder Mailboxes resulting in just three steps:

1) Download the following files from Mail-enabled Public Folders – directory sync script

  • Sync-MailPublicFolders.ps1
  • SyncMailPublicFolders.strings.psd1

2) On Exchange Server, run the following command to synchronize mail-enabled public folders from your local on-premises Active Directory to O365.


Sync-MailPublicFolders.ps1 -Credential (Get-Credential) -CsvSummaryFile:sync_summary.csv

3) Enable the exchange online organization to access the on-premises public folders. You will point to all of you on-premises public folder mailboxes.


Set-OrganizationConfig -PublicFoldersEnabled Remote -RemotePublicFolderMailboxes PFMailbox1,PFMailbox2,PFMailbox3

Issues When Configuring Hybrid Mode

There are a few things to be aware of with this process though, particularly the final step.

1) Remember that the new Public Folders are stored in User Mailboxes which are associated with AD user accounts. If you aren’t syncing your entire Active Directory forest then the Public Folder Mailbox objects may not be synced to Exchange Online. So where are these stored by default? Well the Users container in your exchange enabled domain of course.

It’s likely that you haven’t synced this but you CAN move these objects to an OU that is being synced without any impact. Unfortunately this requirement isn’t included in the documentation. If these objects aren’t synced to Exchange Online then you’ll get the following message


Set-OrganizationConfig -PublicFoldersEnabled Remote -RemotePublicFolderMailboxes PFMailbox1
Couldn't find object "PFMailbox1". Please make sure that it was spelled correctly or specify a different object.
    + CategoryInfo          : NotSpecified: (:) [Set-OrganizationConfig], ManagementObjectNotFoundException
    + FullyQualifiedErrorId : [Server=SYAPR01MB2717,RequestId=d79eaa00-ff32-4076-8791-54ba22e3cb76,TimeStamp=26/11/201
   8 7:13:26 AM] [FailureCategory=Cmdlet-ManagementObjectNotFoundException] C4302B7C,Microsoft.Exchange.Management.Sy
  stemConfigurationTasks.SetOrganizationConfig
    + PSComputerName        : outlook.office365.com

2) Once you’ve moved the public folder mailbox objects remember that the -RemotePublicFolderMailboxes PFMailbox1,PFMailbox2,PFMailbox3 syntax is referring to the Public Folder Mailboxes and NOT the public folder names. You can find these in the ECP under Public Folder Mailboxes.

3) You also need to list all public folder mailboxes in the one command. If you add an additional public folder mailbox in the future then include all the mailboxes and not just the new one.

4) Finally remember that your on-premises address book is different from your online address book. This means that any new mail enabled public folders will only appear in your online address book if you sync them using the Sync-MailPublicFolders.ps1 script. If users can create these objects then you may want to think about scheduling this task.

Only users who have been created on-premises and migrated to Exchange Online can access the on-premises Public Folder store. Only these users exist in the on-premises address book used to authenticate access.

It may not seem that way but ultimately this is a simple service to configure with just a few little gotchas to be aware of.