Offline address book in Exchange 2013
Outlook cached mode Þ Cached mode is the new default configuration for Outlook. Þ It provides an experience that is similar to the offline configuration in earlier versions of Outlook. Þ When you are running in cached mode, your Exchange mailbox is synchronized to a local file (an .ost file), and the offline address list from your Exchange computer is synchronized to a collection of files (.oab files) on your client computer. Þ Therefore, network communication between Outlook and Exchange is significantly reduced. Why offline address book is important? Þ The offline address book contains a set of all the properties of a user that Outlook requires. Þ With an offline address book, Outlook does not have to connect to the global catalog to resolve names.