How can we make it so that every time that a user types the first few characters of a user's name or email address within the address bar Outlook 2016 will automatically search the user's Outlook contacts and then suggest email address auto complete entries based upon the user's Outlook contacts.

We have several users who have lots of Outlook contacts and when they type in the first few letters of the user's names or email addresses within the address bar the users whose email addresses they are looking for don't appear in the email address auto complete suggestion lists.

The email server is Office 365.

How can this be fixed?

Or are there any utilities or software programs that will prompt Outlook 2016 to search through all existing contacts to provide relevant email address auto complete suggestions?