This is called the Offline Address Book and is being generated on the Exchange server.
Due to various synching schedules, it can take up to 48 hours before you could actually see a change in Outlook after a modification has been made on the Exchange server or in Active Directory.
In that case the whole OAB is being downloaded again.
In a later section, it is explained how to modify this.
This can be beneficial to other community members reading the thread.
When you have Cached Exchange Mode enabled, Outlook by will by default cache the main Global Address List as well.
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Learn how to configure the offline address book (OAB) update interval in Exchange 2016.
In this guide, the relevant timings are explained and instructions are given in how you can directly force an update and resync, which can be very handy when troubleshooting or when you work in an Exchange environment which sees a lot of user mailbox mutations.
This means that in the worst possible scenario, an update to the Address Book won’t become available to the user until 48 hours after the change.