Include Additional Email Addresses on Email-to-Case Auto-Response Messages
For example, a customer might submit a case about a problem with the copier in his office before leaving the office for the weekend. That customer might Cc colleagues who will be on site over the weekend and are available to work with your support department to resolve the issue. If you’ve enabled the option to include Cc’ed addresses on the auto-response message sent when the case is created, the customer’s colleagues will receive the case number and can be included on other emails about the issue, making it more likely the case can be resolved and closed quickly.
To enable this option, select Send response to all recipients on the rule entry edit page for an Email-to-Case auto-response rule. For more information, see Set Up Auto-Response Rules.

