Offline address books in Exchange Online
An offline address book (OAB) is a downloadable address list collection that Outlook users can access while disconnected from Exchange Online. Admins can decide which address lists are made available to users who work offline.
Offline address books are generated every 8 hours.
For more information about address lists in Exchange Online, see Address lists.
For OAB procedures, see Offline address book procedures.
Looking for the Exchange Server version of this topic? See Offline Address Books in Exchange Server.
How users download offline address books
In Outlook, click File > Account Settings > Download Address Book.
On the Offline address book dialog box that's displayed, make the following selections:
Download changes since last Send/Receive: By default, this check box is selected. Unchecking this box causes a full download of the OAB.
Choose address book: This drop-down list will display the offline address books that are available to you. Depending on what an admin has configured, you might see only one value here (for example, the global address list).
Click OK. The OAB is downloaded and saved on your computer.
Conditions that cause a full download of the OAB
There are situations where Outlook will always perform a full OAB download. For example:
There's no OAB on the client computer (for example, this is the first time you've connected to your Exchange Online mailbox in Outlook on this computer).
The version of the OAB on the server and the client don't match (a more recent version of the OAB is present on the server).
One or more OAB files are missing from the client computer.
A previous full download failed, and Outlook has to start over.
When a user has multiple MAPI profiles on the same Outlook client computer and they switch between the two profiles that both use Cached Exchange Mode, multiple full OAB downloads of the same OAB files will occur. Outlook supports only one OAB per user account on a computer. If you have multiple profiles, only one profile can download the OAB. If you have to use two or more profiles that use Cached Exchange Mode, make sure that one of the profiles is configured to not download the OAB.