There are many reasons why a Public Folder migration may stop with a failure. The following are some general steps that fix common problems that can occur when performing Public Folder migrations.  If you are getting a specific error message, you can also try the troubleshooting guide linked to that error (if applicable)

Fixing Office 365 Problems:

1. ​Log in to the Microsoft 365 portal as the Admin being used in the migration project.
2. Make sure the user is an administrator. (There will be an Admin tab present in the upper-right menu). If the user is not an admin, then assign the user the global admin role.
3. From the Admin tab, select Exchange.
4. Click on the Public Folder option in the left panel.
5. Click on the Public Folder Mailboxes topic in the top menu.
6. Make sure there is at least one Public Folder mailbox listed. If there are no Public Folder mailboxes, create one to hold the Public Folders being migrated.
7. Click on the Public Folder topic in the top menu.
8. Click on the ... (More) button from the set of actions, and then select Root Permissions.
9. Make sure that the admin user is listed as an owner. If the admin user is not listed as an owner, then add them and apply the change to all subfolders.
10. Make sure there is an Outlook tab. If there is no Outlook tab for the admin user, assign the user an Microsoft 365 license.
11. Verify the mailbox can be viewed by clicking on the Outlook tab.
12. Go back to the Microsoft 365 Admin Dashboard.
13. Click on the Users and Groups option in the left panel.
14. Select the admin user and ensure the following:
• The admin user is a valid active user.
• The admin user has an Microsoft 365 license assigned.
• The admin user name is not misspelled.

Fixing On-Premises Exchange Problems:

1. Log in to the Outlook Web Access portal​ as the admin user being used for the migration project. If it won't authenticate, make sure that the user name and password are not misspelled.
2. Verify that mailbox content can be viewed.
3. Make sure that the admin account can open the Public Folders and Public Folder mailboxes being migrated.
4. Make sure that the admin account has owner permissions for all Public Folders being migrated (root folder permissions are required).