There are different ways to send invoices

• Post: the invoice must be printed and sent by mail
• Manual email: the invoice can be sent by email, but it is not sent automatically
• Automatic email: the invoice will be sent automatically once it is generated. 

The invoice is always sent to the financial email address. If this is not filled in, it will be sent to the regular email address. If you choose automatic email, the email address on the customer card becomes a mandatory field. 

For each customer, you can choose their preferred delivery method. You can set this on the customer card. 

The default value when creating a new customer can be set. See also article Customer settings