You can send invoices by email to multiple contacts: customers, managers, etc.
To send an invoice by email to several recipients in a message generated from the email template
On the Operations tab, click Invoices, and then on the Invoices page, in the Action column, point to the Select button, and then click Send Email.
Enter the appropriate email addresses separated by semicolon in the Recipients box, and then click Send.
To send an invoice by email to several recipients in a custom message
On the Operations tab, click Invoices, and then on the Invoices page, in the Action column, point to the Select button, and then click Send Custom Email.
On the Email Message page, enter the appropriate email addresses separated by semicolon in the To box, enter message details, and then click Send.