Set the Global Address List as the Default Address list in Outlook 2016/365
When searching for email addresses, sometimes you will find that you can't find any of the names you are searching for. This is probably because your default address book is your personal address list rather then the Global Address list populated automatically when an account is created. Here is how to change it:
On the Home ribbon in Outlook, go to the far right side and click on Address Book.
Then click on Tools. → Options...
Under When sending e-mail, check the address in this order select Start with Global Address List
Also under When opening the Address Book, show this address list first, make sure Global Address List is selected
Now click OK to confirm the new settingsYou can close the address book window now