How do I change a data field from being optional to mandatory?

How do I change a data field from being optional to mandatory?Side Note:
An Asterix next to a data field symbolises a mandatory field.
Customise interface (Interface management) permission is needed to complete the steps.

For an example, I will change the voluntary email address to become mandatory.�Hover your mouse over Administration and click customise interface.

Click on the + sign for Person, Contact details, Fields and then finally Edit Emails.

In the �Required� dropdown, click True and then save the changes by clicking on update.

As you can see, the �Email addresses� field is now mandatory.

Users will not be able to save until data has been entered into the mandatory field.