Action
To update your offline address book, Outlook app's synchronized copy of the Global Address List (GAL), to assure that it has the latest updates, follow the steps below.
Outlook automatically updates the address book periodically, usually once every 1-3 days.
Instructions
When a change is made to a contact in the system of record, it is not instantly reflected in Outlook since Outlook is looking at an offline copy of the Address Book by default. The mail system produces an update file once a day at 5am. Once the update file is created, Outlook will automatically download the update on a random schedule roughly every 24 hours, but you can force Outlook to download the new file by following these simple instructions.
Select the File tab located at the top left of Outlook.
Select the Account Settings button.
Select Download Address Book...
Verify the checkbox next to Download changes since last Send/Receive is checked and select OK.
Once you select OK the following window will appear.
Once this completes, you have successfully updated your Offline address book.