Public Folders in Microsoft Exchange
Public Folders has long been a feature in Microsoft Exchange as a way to help facilitate collaboration amongst users well before collaboration tools hit the market.
Public Folders offer an ability to create folders where files and emails can be placed into them and access granted to groups of users for common access. You can also mail-enable the folders, allowing them to send and receive mail using a simple alias. All of this is available through using the Microsoft Outlook Client, which makes it that much more appealing as a one stop application for these needs without having to roll out a separate client.
Because Public Folders have been around for a long time, companies have embedded organizational processes into them as the very fabric of how they operate day to day. They use them as a central repository for team data, or for project managed activities as examples. Over time, the number of folders contained could number in the tens of thousands and data in the Terabytes spread amongst multiple Exchange servers.
How Public Folders Have Evolved
Maintaining Public Folders over time has also shown to be problematic, as versions of Exchange up through 2010 had them stored in dedicated databases outside of where mailbox data was stored, so you did not have the ability or flexibility of using DAG’s (Database Availability Groups) to provide high availability and disaster recovery. You could get around this by custom scripting, but not having it by default imposed additional administration burden.
Public Folders were since included as part of the DAG as of the release of Exchange 2013.
With Exchange 2016, you can support up to 1 million Public Folders. However, because it’s part of the DAG and uses Mailboxes to store the Public Folder hierarchy, you need to be aware of how much space is being consumed per public folder mailbox as this can impact accessibility to your end users.
Moving Public Folder Content to Microsoft 365
Organizations can now move Public Folder content to modern Microsoft 365 destinations such as SharePoint Online and Shared Mailboxes, reducing reliance on on-premises Exchange infrastructure while modernizing collaboration.
The significant gains in administrator productivity are evident, where the pressures of maintaining high availability and disaster recovery for your Public Folder hierarchy are in the hands of Microsoft. Exchange Online is even able to automate mailbox splits, so when your Public Folder mailbox approaches the 100GB quota limit, it will automatically partition it into another mailbox.
As mentioned previously, with most organizations having business processes tightly wrapped around Public Folders, keeping them accessible and protected from disaster is paramount.
However, moving Public Folders to Office 365 Exchange Online does not completely absolve administrators from keeping tabs on them. Some conditions must be strictly followed to keep Public Folders accessible, so knowing them beforehand is critical.
These conditions are not only necessary for maintaining a working Public Folder environment but also play a crucial role in migration planning to Exchange Online, as failure to account for them can severely set back your migration efforts.
Planning Your Public Folder Transition
When planning to move Public Folder content to Microsoft 365, it would seem that the migration should be straightforward as long as you understand the requirements and have planned for them. In reality, it is anything but easy.
If you are migrating from Exchange 2010, for example, you will be faced with a cumbersome script-based Public Folder Transition process that can be daunting for even the most seasoned administrator.
Even if you can manage the scripting operations, you still need to map your Public Folder hierarchy to be compatible with Office 365. Depending on the size of your environment, this can become an extremely time-intensive task.
In addition, you need to understand Exchange Online limitations, including sub-folder limits that do not exist in on-premises Exchange.
Transfer Performance
Once your Public Folder hierarchy has been mapped correctly, you then need to prepare for the actual migration.
Depending on the version of Exchange you are migrating from, migration speeds can be much slower than anticipated. For example, Exchange 2010 commonly transfers between 5 GB and 10 GB per hour. If you have terabytes of Public Folder data, expect the migration to take days—or even weeks.
The other aspect of the migration is whether users should continue creating new Public Folders and adding content during the migration. If your migration will take days or weeks, locking users out for that entire period may not be acceptable to the business.
If that is the case, you will need to prepare for multiple migration passes to synchronize the changes (delta) between migration runs, and the comparison between those runs is typically a manual process.
Conclusion
Moving Public Folder content to modern Microsoft 365 destinations requires careful planning, especially when preserving permissions, folder hierarchy, and business workflows. With the right strategy and tools, organizations can modernize their collaboration environment while minimizing disruption.
The following is an excellent presentation given by Microsoft MVP Peter Schmidt regarding how to migrate your Public Folders to Office 365 Exchange Online.
