When trying to sync Public Folders to Exchange 2013 and above using a secondary Public Folder mailbox, the following errors may occur in the Public Folder Target Agent log (EMWPFTA.log) on the Target Agent Host:
Beginning with Exchange 2013, the first Public Folder mailbox created will be the only writable copy of the Public Folder Hierarchy.
There are two types of public folder mailboxes: the primary hierarchy mailbox and secondary hierarchy mailboxes. Both types of mailboxes can contain content:
Primary hierarchy mailbox: The primary hierarchy mailbox is the one writable copy of the public folder hierarchy. The public folder hierarchy is copied to all other public folder mailboxes, but these will be read-only copies.
Secondary hierarchy mailboxes: Secondary hierarchy mailboxes contain public folder content as well and a read-only copy of the public folder hierarchy.