After creating your invoice, you can email directly your invoice by populating Email field on the right of your customer name. QuickBooks Online makes it easy to add a second email on the fly: enter your first email address, followed by <comma><space> second email address. You can add multiple emails as you wish separated by <comma><space> between email addresses.
In the example below, we have two emails in the Email field. Press "Save and send" bar to save your invoice and send email.

QBO Adding Multiple Emails on Customer Invoice 1


You can also set customer email by selecting Customers from left pane > double click the customer you intend to enter the email > click Edit to open Customer Information window:


QBO Adding Multiple Emails on Customer Invoice 2


Then enter the customer email address in the Email field provided shown in blue above and click Save. This way, each time you create invoice for your customer, the Email field is automatically populated.

If you need to send a copy of email sent to yourself, select Gear Box > Company Settings > Form Delivery > Email Message > check the “Copy me of all forms sent by email” box:


QBO Adding Multiple Emails on Customer Invoice 3