How to add optional attendees in outlook Meeting/Appointment

In outlook when ever we schedule a meeting we will add mandatory attendees and some of them may optional. Let see how to add options attendees.

Click on New Meeting and type the list of recipients in the to list. Now Click Scheduling Assistant

In the left hand side we can see the list of attendees we added and we can see small icon between email and check box. Click on that icon and we can see the options to make mandatory or optional