The Public Folder Mailbox was created using Exchange Management Shell, using the
-HoldForMigration parameter.
New-Mailbox "PFMB1" -PublicFolder
-HoldForMigration -database "MailboxDatabase"
The
-HoldForMigration parameter prevents any client or user, except for Microsoft Exchange Mailbox Replication service (MRS), from logging into a public folder mailbox.