"The Offline Address Book contains the properties of a user, such as e-mail addresses, that Microsoft Outlook requires in order to send an e-mail message and display information about the user. By using the Offline Address Book, Outlook does not have to connect to Exchange in order to resolve names or open the records for each user. This reduces network traffic and improves performance."
This guide will show you how to download the Offline Address Book in Outlook 2016 using Windows 10.
Open the Outlook mail client.
Click the Send/Receive tab, then Send/Receive Groups > Download Address Book...
Next, you will be prompted to choose an address book, which should default to "\Offline Global Address List." Click OK.
Download changes since last Send/Receive
To download the entire address book, uncheck the Download changes since last Send/Receive box. If this is your first time downloading the address book, you may leave this box checked and the entire book will still be downloaded. Leaving this box checked can also serve as a way to manually update the address book.
The book will download and be stored in C:\Users\UserName\AppData\Local\Microsoft\Outlook\Offline Address Books, however, the .OAB files found within don't actually do anything if you try to run them. These files run in the background, concurrently with Outlook.