Hi dan198,
Thanks for reaching out here. Welcome! It's important that you're able to create sales forms with the associated email addresses for your customers. QuickBooks Online provides the option to set additional information by default and save valuable time. I'd be happy to provide more information so you can complete your QuickBooks goals in a timely fashion!
Due to the limitations when using the QuickBooks Online app, I recommend logging into your account from a web browser. Once you've logged in, follow these steps to set additional default email addresses to your customer(s).
1. Open Sales and then Customers from the left menu
2. Select the Customer and hit Edit
3. Scroll to the email section
4. Enter the two email addresses, separated by a comma and space
5. Hit Save
If you require additional assistance, please contact us. Your success is our number one priority and we'd love to help!