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Public Folders in Office 365 Exchange Online, a New Beginning

Public Folders in Office 365 Exchange Online, a New Beginning

Exchange 2013 and Office 365 Exchange Online public folders have changed for the better.  Instead of being an aspect of email creates administrative headaches from a recovery and redundancy perspective.  They have become part of the traditional mailbox DAG design creating more of an acceptance by Exchange administrators.  Regardless of what was going on with the challenges surrounding the backend design users typically love them.  Public Folders provide a simple access to corporate or team shared information right within the Outlook or Outlook Web App interface. 

Considering the Limits

This article will focus on the Office 365 Enterprise plans.  There are Office 365 standalone plans available, but many of the limits are different.  If you are looking at a standalone plan be sure to check out this article before finalizing your Office 365 public folder decisions.

That being said, let’s focus on the Office 365 Enterprise plan and what Microsoft offers for your organizational public folders needs.  First up, they allow up to 50GB of public folder data per public folder mailbox up to 50.  This means that that the maximum total size your organization can use for all of your public folder mailboxes is 2.5 TB.  This 2.5 TB of data can hold up to 100,000 public folders.  Honestly, 2.5 TB of public folder data is quite significant and in most cases it is difficult to consider this a limitation, but I am sure there is an organization somewhere that will not be able to move to cloud-based public folders even with this amount of capacity. 

For public folders that are mail-enabled and can send/receive email here is a list of the limits you may need to consider.   When sending or receiving a message the size limit is 25 MB, which is really a quite reasonable limit; however, I have seen organizations that allow 40 and 50MB size messages.  The file attachment size limit is also, 25MB.  For both of these cases, this limit will encourage the need for alternative means of file transmittal such as FTP or other methods. 

Other considerations surrounding limits revolve around some of the measures that can protect our cloud-based email environment especially with mail-enabled public folders that receive external email.  One of many layers to protecting your environment from spam and mail-mailing worms/viruses is that Microsoft has implemented imposed mailing limits.  They are as follows for organizations that have an Office 365 Enterprise plan. 

The above limits and additional detail about Office 365 plans can be found in the Microsoft Technet library.  Here is a great resource with additional information on this topic.

Now Let’s Get Into the Real Details

Regardless of whether your organization will migrate its public folders to Exchange Online a primary public folder mailbox will be required to get started.  Also be aware that if the data in your public folders increases above the capacity allowed within public folder mailbox quotas, Microsoft automatically creates new public folder mailboxes.

Additionally, in order to do public folder work within Exchange Online your administrator may need to verify that you have the appropriate permissions.  See the table below that highlights these requirements.


Mail-enabled Public Folders

Organization Management or Recipient Management

Public folders in general

Organization Management or Public Folder Management

With that let’s get started with our first public folder mailbox!

  1. Sign in to Office 365 through
  2. Click Admin

  1. On the left side of the screen click Exchange

  1. Click Public Folders

After “public folders” has been selected there will be a notification as shown below that states that a public folder mailbox is required in order start any work with public folders.  See the image below.

  1. Click Public Folder Mailboxes


  1. Click the + sign



  1. Type the name of the public folder mailbox and Click Save


  1. You may receive the following warning when creating the public folder, just click OK

Note:  This warning doesn’t prevent the creation of the mailbox, just a delay in the process for backend replication.


  1. Once the public folder mailbox is completed it will appear in the list similar to what is shown below



Next Step, Let’s Create Some Public Folders

  1. While still in the Public folders section in Exchange Online.  Click Public Folders as shown below
  2. Then click the + sign to start the process of adding your first public folder


  1. Give the public folder a name and then click Save


  1. After saving, the public folder is created. 

Note:  The new folder will require new permissions or even may need to be mail-enabled.  We will first mail-enable the folder.

  1. On the right side of the screen while the public folder is selected you would click “enable” to start the mail enable process. 



  1. Then click Yes to complete the process


  1. When complete it can be seen as enabled


  1. Now let’s take a look at the permissions.  Under Folder permissions, choose Manage

  1. Click the + sign to add new permissions



  1. Click the Browse button




  1. Choose the user or group that these new permissions will apply to and then click OK


  1. In this case we will select “Publishing Editor” permissions, but your organization can apply whatever rights are relevant for the user or group that will have access to the folder.  This can be anything from Owner to View Only access and is completely up to you.  Once the permissions are selected, click Save.


  1. Click Save again



  1. Click Close




  1. This completes the process for setting up a new public folder in Exchange Online


Public Folder Migrations

For migrations, while a primary public folder mailbox will still be required the steps for migrating public folders will be different.  Here are a couple of resources that will get you started with this process.




Before Exchange 2013 and Exchange Online, Public Folders have been referred to as the cockroaches of Exchange, for me they have always been the “necessary evil”, and for some administrators just the thought of them makes them cringe.  But with public folder mailboxes, Microsoft is recreating the image of public folders.  It appears that this is a new beginning for public folders through a more reliable and supportable design.  Enjoy!  

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