Hello SalesMan,
There are techniques that you can try that I found in another forum post here. In summary, the idea is to create a contact for the company that holds the emails of all the contacts that receive the estimate. For the email field you have each email address separated by a ';' mark. Also, any contact for the customer who has there 'Opt out of billing...' unchecked will get the estimate. You can find the option under Edit Contact ...in the Customer screen.
There is also a Help Center article on Estimates that relates to your question that can be found here.
- Greg