Moving Legacy Public Folders to Office 365

Public Folders are a long-standing feature of Microsoft Exchange that work as a central data repository for team data. Exchange Public Folders were initially designed to facilitate team collaboration, enable users to access data anywhere, and allow users to manage folders without system administrator involvement. As Public Folders evolved, they added newsgroups connections, and Exchange version 5.5 included the ability to add an SMTP address, so each mail-enabled Public Folder could send and receive mail.

There are two types of Public Folders, the version of Exchange will determine the kind that they are.

Legacy Public Folders – Exchange 2010 and lower
• Separate Database from Mailboxes
• Separate replication schedule
• Exchange Version to migrate to Office 365
  • Exchange 2010 SP3 RU8 or later

Modern Public Folders – Exchange 2013 and higher
• Hierarchy
  • Each Public Folder mailbox has a copy of the Public Folder hierarchy
  • There is only one writeable copy of the hierarchy at any given time
  • Clients connect to their home hierarchy
• Content
  • Public Folder content is stored in a Public Folder mailbox
  • It is not replicated across multiple Public Folder mailboxes (although passive copies of the mailbox are supported through high availability services)
  • All clients access the same Public Folder mailbox for a given set of content
• Exchange Version required to migrate
  • Exchange 2013 CU15 or later
  • Exchange 2016 CU4 or later

Legacy Public Folders are an older technology and are stored in a separate database outside the mailbox database. They required separate EDB files that are replicated to another Public Folder server in other sites, so the data was available to users within the organization. The replication multi-master model and changes pushed to all servers housing the Public Folder database.

Microsoft’s intent was to eventually phase-out Public Folders instead of hoping users would use Microsoft SharePoint instead. They eventually relented from the pressure from Exchange MVP’s and other customers.

Microsoft then took the approach of modernizing Public Folders while maintaining the end-user experience. Microsoft introduced Modern Public Folders in Exchange version 2013. Instead of having a separate database, it was built on the mailbox infrastructure using mailboxes to house the Public Folders. IT administrators no longer needed to learn two management approaches for mailboxes and Public Folders.

Public Folders are now supported in Office 365. The process to migrate is easier for migrating Modern Public Folders to Office 365 Public Folders and you have choices. You can do a direct migration to O365 to investigate Office 365 group Folders for some or all your on-premises Public Folders.

It is, however, a bit trickier to migrate Legacy Public Folders to Office 365 Public Folders. We will focus on what’s required to achieve that goal. Some of the aspects of migrating legacy Public Folders to OFFICE 365 are the same as if you migrate your legacy Public Folders to Exchange 2013 (or higher) modern Public Folders.

Office 365 Public Folders limits vary on your licensing, so this needs to be considered when planning your Public Folder migration.

Storage limits across O 365 options

(as of 1/9/2020)

Office 365 Exchange Online supports up to 500,000 folders in the Public Folder hierarchy.
The trick is they have to fit within a max of 1000 Public Folder mailboxes. Depending on your license type, the Public Folder mailboxes can be up to 50 GB in size for Business and Enterprise E1 tenants, or up to 100 GB for Enterprise E3 and E5 tenants.

You cannot move from legacy Public Folders to Exchange Online until all mailboxes are on Exchange 2013/Exchange 2016 or Exchange Online. For this reason, the migration of legacy Public Folders is usually the last task on a deployment list. It goes without saying that the very first task is to review all the Public Folders and to clean out what is not needed. Your Office 365 license comes into play again.

Another item to check is to verify all the mail-enabled Public Folders and remove the email addresses of ones that are no longer needed. Another issue to be aware of is Send-as and Send-on-behalf permissions are not migrated with the Public Folders, so you will need to audit those permissions and manually reapply them after the migration is complete. This can be addressed by creating scripts to reapply the permissions.

Microsoft’s recommended migration method is to migrate user mailboxes before Public Folders. Cloud-based mailboxes can access Public Folders stored on older Exchange on-premises servers as long as Outlook clients are used. OWA does not support the redirect mechanism used to access on-premises Public Folders. So, if you are considering F1 or E1 licenses you will need to migrate the Public Folders at the same time as the mailboxes since these licenses only allow online access.

The attraction of moving user mailboxes first is that people get faster access to the new features available in Office 365 and it might be possible to reduce costs by eliminating many on-premises mailbox servers. On the other hand, moving mailboxes usually represents the bulk of the migration effort and it will take longer to plan and execute.

Click here for the Microsoft site that contains the Public Folder migration scripts.

Third-party migration utilities

Microsoft is not the only source of Public Folder migration tools. Whenever possible, you should consider the tools Microsoft makes available, because they’re free. But other tools are available from third-party providers that might be more effective at handling a specific situation. For example, the basic migration facilities available from Microsoft don’t accommodate the parallel migration of both content types because this functionality needs bi-directional Public Folder coexistence, which is not a feature Microsoft has engineered for Office 365. In this instance, you’ll need to use a third-party product that can perform the bi-directional synchronization for both Public Folder hierarchy and contents. Some third-party tools can prune and graft Public Folders as the migration is ongoing, which is an attractive choice when you need to migrate a massive Public Folder infrastructure.

Below is a list of possible tools that could be of assistance in moving Public Folders. This list is not meant to be an exhaustive list of tools, nor a specific endorsement of one tool over another, just a launching pad to help you, the dear reader.

BitTitan MigrationWiz is the tool I have used to migrate clients Legacy Public Folders to Office 365 Public Folders. They provide many guides and scripts, depending on your current environment, including the following:

• Public Folder Migration Guide From On-Premises Exchange 2007+ to Office 365 < 20GB
• Public Folder Migration Guide From On-Premises Exchange 2007+ to Office 365 > 20GB
• Public Folder Migration Guide From On-Premises Exchange 2007+ to Office 365 < 20GB Hybrid mode
• Public Folder Migration Guide From On-Premises Exchange 2007+ to Office 365 > 20GB Hybrid mode

1. Prepare Source Environment
2. Prepare Destination Environment
3. MSPComplete Steps
4. MigrationWiz Steps

Whether you use Microsoft’s scripts or a third-party tool, the two tasks that should be performed once the migration has been completed is to reapply mail-enabled Public Folder email addresses and reapply the send as permissions.

The big take-away in considering migrating your legacy Public Folders is if they are needed. The easiest thing would be to find other places they could be stored. Most likely, that kind of analysis is going to take time, more time than some organizations will be able to commit. Exchange 2010 is out of support in October 2020, so the clock will force your hand. We at Anexinet would love to assist with any Public Folder migrations you need help with. Please take a moment to check out our Office 365 Migration Strategy Kickstart, which accelerates your migration with a proven approach that ensures high adoption and guarantees success. Arm your organization with a plan and road map to optimize and accelerate your Office 365 migration in just two weeks.