A new email address may not appear in Outlook’s Outlook Global Address List. The below video and proceeding guide will go through how to force the Address List to sync.
In Outlook, select the Send / Receive tab.
Select Send/Receive Groups, and then Download Address Book from the drop-down menu.
This will open a little pop-up window. Make sure the \Offline Global Address List is select and select OK.
Outlook will start the process. This should only take about a minute.
Once it's complete, your address list will be updated. You may need to close and restart Outlook.
Note: The address list does automatically. It can take up to 48 hours from initiating the update for the update to start and complete. See Administering the offline address book in Outlook (microsoft.com) for more information.
For more information, please visit the Microsoft 365 Resources on the Patriot Knowledge Center.