If a customer does not have an email, he must ask a person that has one to buy the tickets for him, or he must contact you so you can take the order for him over the phone or on the spot with your dealer's ticketing that offers more option - read on.
Reservation by the Merchant
If you place an order for a customer who does not have an email to receive confirmation that includes their order and tickets, then you must use the "None" option for the customer's email. On the other hand this customer will not be able to receive any email after having completed the order. To find his order, go in the Action menu to print the order and the tickets to hand him or send them to him by mail. Choosing None as an email will generate a single internal email for this client because the email is the customer ID and must be unique and not empty.