Hi all,
Version 7.8 has now reached public release candidate, which includes this feature: https://preview.whmcs.com
A new option called "Auto Add Carbon Copy Recipients" has been added to Setup > General Settings > Support tab, controlling this feature.
Please join us during the pre-release testing period and provide your feedback in our dedicated beta community board: https://whmcs.community/forum/471-v78-beta-discussion/