Public Folder Limits in Office 365 Exchange Online.

Office 365 Public Folder mailbox limits and what they mean for migration

Microsoft’s Office 365 Public Folder mailboxes are the new home for legacy or any Exchange on-premise public folders.

But not so fast!

Sizing limits of Office 365 Public Folders are important to consider before doing a migration. Your current public folder hierarchy may not fit so nicely into the “modern” Office 365 Public Folder Mailbox architecture that Microsoft has designed.

Public folder mailbox sizing limits in Office 365 are important considerations before doing a migration. Here are some of the limits that you need to consider (as of May 2023):

  • Max. number of public folders: 500,000
  • Max. number of subfolders in a public folder: 10,000
  • Max. number of items per folder: 1,000,000
  • Max. number of public folder mailboxes: 1,000

The size of each public folder mailbox is based on your license type. For example, if you have Exchange Online Plan 1 license you will be limited to 50 GB per Public Folder Mailbox. For Exchange Online Plan 2 or any of the Enterprise plans, the limit is 100 GB per public folder mailbox.

With 1,000 Office 365 public folder mailboxes at 100 GB, you have a max. data volume of 100 TB for your public folders. That’s fantastic, especially considering that you do not pay for them! Yes, that is right. Currently, any size Office 365 tenant can spin up the maximum public folder mailbox allowance.

For smaller companies with only a few hundred gigabytes of public folders, the limits on public folders are not an issue. However, for larger organizations, these limits present a real challenge. Not only is public folder migration to Office 365 a challenging process to begin with, but now you need to worry about transposing your legacy public folder hierarchy with these restrictions in mind. To even begin down that path, you need to have analytics on your current public folders.

Only a few short years ago, the number of public folders you could create and the size of the public folder mailboxes was much smaller. Over the years, Microsoft has increased this to make it close to matching what you can do with public folders in Exchange 2016 or 2019.

However, regardless of the amount of data you have in your public folders, the number of public folders can still be a factor. We have seen companies with less than 200 GB of data surpass some of the limits, such as the total number of items per public folder or the max number of direct subfolders. Not having a TB or more of data in public folders does not mean you can ignore the limits.

If smaller organizations come close to the limits, you can bet the bigger companies will hit them every time.

Any sizable public folder hierarchy (10 TB and greater) might exceed the 500,000 public folder limit. This restriction on the public folder count means that larger enterprises have a bigger project on their hands to dig into their current folders to decide what needs migrating and what can be archived or deleted. For instance, we recently spoke with a firm that has over 2,000,000 folders in their current hierarchy, but less than 100 TB. They obviously have a big cleanup job before migrating, and their migration will likely entail removing data and moving it to other destinations.

Here is what you need to be smart about sizing limits when you migrate public folders to Office 365:

  • Analytics – You need insight that can give you the full picture of your legacy public folders. Maybe you have iTunes Libraries sitting in public folders that aren’t worth migrating.
  • Intelligence — The insights you gain from analytics need to be actionable in the migration process. Not by you. The software should have fancy algorithms that use insights to simplify the migration process.
  • Sizing Automation – You should not have to manually create Office 365 public folder mailboxes for the migration, and worry about what migrates where.
  • Sizing Optimization – To get the most out of your public folder mailboxes, the migration should allow you to optimize the structure of your content automatically.

Microsoft has been trying to phase out public folders since SharePoint came along. The reality is that they are mission-critical for many businesses, and because of client demand, Microsoft has been forced to keep them going. In fact, as of May 2023, the interface for browsing public folders in the Exchange Admin Center was updated.

Modern Office 365 public folders are a great solution, especially if you are migrating legacy public folders into Office 365 and you want a seamless transition for your users. With most companies able to take advantage of the 100 GB public folder mailbox limit, migrating your public folders just got that much easier.

If you have concerns about your public folder migration bumping into the Office 365 sizing limits, you can contact us to speak with a technical specialist for some ideas on how to tackle it.

Become An Exchangesavvy Partner

Enhance Your Service Offerings With Proven Solutions.