After migrating from example Exchange 2007 to Exchange 2010 or 2013, your clients might loose the public folders on their Outlook/ OWA. Although the public folders are on the new server and healthy, they won’t show on the client side.
This is most probably because the Public Folders on the new servers are not assigned to the mailbox databases and are still refering to the old servers.
Open the Exchange Management Console
Expand Organization Configuration
Open Mailbox Node
Open the Database Management Tab
Right Click the Database in question and select Properties
On the new window expand the Client Settings field
You may notice on the Default Public Folder Database text box something similar to the below:
mydomain.local/Configuration/Deleted Objects/Public Folder Database
This is pointing to a deleted Public Folder Database.
To fix this, click on the Browse button and select the new public folder from the populated list. Once ready you will see that the entry changed reflecting the new selection.
Close the client’s Outlook and re-open it. You will be able to see the folders.