BCC stands for "Blind Carbon Copy" and provides you a copy of all communications and forms sent out of 17hats. This can provide additional assurance and communication history that your email was sent. Your clients will never see your email address copied on the email itself.
To enable this option go to: "Account Settings", "Email Settings":
There is a checkbox for "BCC you on all outgoing email". By default, the option is disabled, to enable it, check the box.