1. Opened Outlook and set to work offline.
  2. Created a new email and pressed "To" showing all contacts.
  3. Highlighted all contacts and entered them into the "To" field.
  4. Set subject as "Test" and pressed send email.
  5. Went to "Outbox" and deleted the email so it would not be sent to all contacts.
  6. Set Outlook to "Work Online" and tested, Auto Complete is now working as required.