When Microsoft Outlook users try to access public folders in Exchange Server 2013 or Exchange Server 2016, the following dialog box appears:
However, if the users click Ok in this dialog box, they are not connected to the public folder.
Additionally, the users may receive the following error message:
Cannot expand the folder. The set of folders cannot be opened. The file C:\Users\<username>\AppData\Local\Microsoft\Outlook\filename.ost is in use and cannot be accessed. Close any application that is using this file, and then try again. You might need to restart your computer.
This issue occurs because the AutoDiscover service cannot discover the email address that is stamped on the public folder mailbox.
To resolve this issue, use one of the following methods:
Create AutoDiscover-related DNS records for the email address that is stamped on the public folder mailbox. For more information about the Exchange 2010 Autodiscover service, go to the following Microsoft website: