Talvez você esteja procurando a propriedade do Exchange Server de Manter informações lidas e não lidas por usuário para essa pasta descritas por Microsoft como:
When you select this setting for a public folder, the items in the folder change from the Unread state to the Read state for each user when the items are viewed by the user.
However, the state changes from Unread to Read only for the user who viewed the item. When another user views an item that has been viewed by other users, the item appears in the Unread state for that user. When the item is viewed by the user, the item changes to the Read state. Therefore, the Read or Unread state for items is maintained per user. The status is not maintained per public folder.