Hello, Fuling.

I appreciate your clarification and the additional details you provided. Let me share some information on how to set up sales order and Invoice to different email contacts.

You can email sales forms, invoices, and statements to your customers individually or as a batch. 

1. Click dropdown and select Email.

2. Add the email address that you want to include.

3. And Send.

For future preference, you can open this article: Verify that an invoice was emailed and read by recipient.

If you have further questions about setting up multiple emails, feel free to comment down. Take care!