There is a field for BCC in Recruiting's email widget. This allows you to Blind Carbon Copy recipients to the email, meaning they receive the email but do not show up as recipients to other recipients of that email.

Important note: Any email you send from Recruiting is stored in the Candidate History panel and can be read by other users. If you use BCC, we hide the BCC recipients from other Staffing and Standard Users, but the email itself is still visible. Only Admin users can see who was BCC'd on the email when reviewing it in the Candidate History panel.