If a client would like to receive an email copy of their invoice that is created in QBO, this can be set up at the customer level of the account.
Automatically Email invoices when jobs are invoiced. Please note if they pay by check, since job invoices are created before you post their check payment, they will receive an invoice that indicates they owe a balance. This feature is best for your credit card paying customers. Also please note, when customer's set up access to their portal, they can download a PDF of their invoices from there.
PRO TIP -- The invoice will be emailed to the "Preferred Email" on a customers account