In most organizations, the top few levels of the Public Folder structure are designed with some hierarchy in mind. This is done to organize the information, and also to control the replication of information across the network. Generally, the first few levels are designed with a department or geographic organization. Most Exchange administrators usually lock down the top-level folders to prevent the hierarchy from being corrupted by users.
Note: Only users in the following group can create top-level Public Folders: Public Folder Management role group.
The term "top-level folder" can be a little confusing when you look at the view of Public Folders in Outlook. At first glance, a top-level folder appears to be a third-level folder, but this is only because the Exchange Server retains the ownership of certain folders that are created during the installation setup process.
Top-level folders are created under All Public Folders.
Since our licensing is based on either the root folder or the top-level Public Folders, here are some simple examples to make it clear what is considered the root and a top-level folder.
1) The root folder is the folder below the "Public Folders" entry, but above the top-level folders. In the diagrams below, it is both referred to as "All Public Folders" and 'Default Public Folders'. In order to add the root Public Folder to your migration, simply enter a single forward slash ("/") and all Public Folders below that will be migrated. If the size of the folders is greater than 10GB, then multiple licenses will be required to complete your migration, and you should set the "Max. licenses to consume per item per pass" to the expected size you will be migrating (e.g., if you are migrating 55GB of Public Folder data, then six licenses will be required).
2) Here is an example screenshot of how Public Folders are displayed from within Outlook:
3) Here is an example screen shot of how Public Folders are displayed from an On-Premises Exchange 2010 Public Folder (lab) server. The top-level Public Folders are circled in yellow. In this example, if you were migrating from the top-level folders, then you would need to purchase Public Folder licenses for each of the folders circled in yellow. If any of them are more than 10GB in size, you need to purchase the necessary number of additional 10GB Public Folder licenses to accommodate for this size. For example, if the jamesb folder is 24GB in size, then three Public Folder licenses are required in order to migrate this.
4) Here is an example of how Public Folders look when using a Hosted Exchange provider. In the example below the xxxxx.com Public Folder would be considered the only top-level Public Folder, since this is how Hosted Exchange providers structure their Public Folders. Therefore, if xxxxx.com folder was less than 10GB in size, you would only need to purchase one license. If the total of all these folders was, say, 54GB, then six Public Folders licenses would need to be purchased in order to migrate all the folders.