Outlook cached mode
· Cached mode is the new default configuration for Outlook.
· It provides an experience that is similar to the offline configuration in earlier versions of Outlook.
· 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. Therefore, network communication between Outlook and Exchange is significantly reduced.
Why offline address book is important
· The offline address book contains a set of all the properties of a user that Outlook requires.
· With an offline address book, Outlook does not have to connect to the global catalog to resolve names.
Difference between offline address book and the global address list
· The offline address book is a snapshot of the Active Directory directory service information that is available in the global address list.
· some information is available in the global address list that is not available in the offline address book.
· The offline address book does not contain some items that are available in the global address list like custome properties , Organization hierarchy information and Group membership information
· If you are in cached mode and if you are working online , Outlook uses both the offline address book and the global address list to provide a complete listing of user information.
· If you are in cached mode and if your connection status show Disconnected , you can see only the information that is available in the offline address book.
New offline address book features
· Exchange 2003 and later supports a Unicode offline address book.
· The Unicode version in exchange 2013 is also known as Version 4 similer to the exchange 2010.
· Has a filtering mechanism in place that makes sure that only those certificates that are used by Outlook for public key infrastructure (PKI) will be present in the offline address book which significantly reduces the size of the offline address book from servers.
Offline address book updates
· If left constantly running, Outlook in cached mode automatically updates the offline address book on the client every 24 hours.
· Different people will receive updates at different, random times.
· By default, the Exchange computer generates the offline address book files every morning at 05:00.
· If outlook taking long time to download the OAB, It might be the issue of Active directory replication or hard disk slow performance.
Offline address book sizes
· Offline address book sizes can vary from 3 MB to 700 MB.
· Size depends upon usage of certificates in a company, number of users , distribution groups in Active Directory. Full offline address book size is approximately 1 MB per 1,000 users.