In order to migrate public folders to or from Office 365, it is necessary to grant administrator account root-level permissions to public folders. To do this, perform the steps below:
1. Log into the Office 365 admin account.
2. In the top-left corner, click on the grid icon.
3. Click on the gray Admin button to go to the admin center.
4. On the side bar, on the left-hand side, near the bottom, is the ADMIN button. Click on the arrow next to this button to expand the options.
5. Select the Exchange option.
6. Click on the Public Folders link in the lower-center of the resulting page.
7. Now there is a list of your public folders. Above the list, there is a row of icons. One of these icons consists of three dots. Click on the three dots, then select Root permissions from the resulting drop-down menu.
8. In the resulting window, click on the plus sign (+), click Browse, and then select the admin user that will be granted root-level permissions.
9. Select Owner from the drop-down.
10. Make sure all the boxes are checked.
11. Click Save to confirm the changes.