You can use the Customer Validation Rule Settings to configure what pieces of information are required when creating a customer.
In the example above, the user has added email to the list of required fields. Now attempting to create a customer without taking an email will result in an error.
Important: When you make a field required for a customer, you will be required to fill in the field for new AND existing customers when saving a ticket.
Note: Creating a new customer will always require at minimum First/Last Name and Primary Phone Number.