An address book contains user properties, such as job titles, addresses, and telephone numbers that a server makes available to its clients. Clients can browse or search the address book to look for recipient information. To organize the contents of an address book, the server can divide recipients into containers and the client can choose which container to browse or search.
Each address book container is known as an address list. The collection of available containers, or address lists, is the address book. When the client is unable to reach the server, which can be caused by working offline or having high network costs to access the server, the client can use a local copy of the address book or address lists to retrieve user information. The local copy of the address book is known as an offline address book (OAB).
An OAB is composed of three or more files that provide the full functionality of the online address book when the client is working offline. This protocol describes the structure of each of the files that a version 2, version 3 or version 4 OAB require.