Navigate to the Edit page of an Invoice record.
Click the Communication subtab and go to Messages
To be e-mailed checkbox should be checked.
Enter multiple Email Addresses.
Note: This is the box on the right. Users can enter multiple email addresses by separating them with a semicolon. It is important to separate the addresses with only a semicolon and not include any spaces.
Users can enter multiple email addresses and separate them with semicolons. It is important to separate addresses only with semicolons and no spaces.
Click Save.