What does”return CC to” mean?

In an email, the CC stands for “Carbon copy”, which means everyone in the list received a copy of the email message.

Stands for carbon copy- which dates back to the days when typists used carbon paper to make duplicates of letters, for files, or for multiple copies being mailed, before copy machines were invented. If names are inserted in the CC line, these people will also get copies of the email that you have written. So if you send an email to Frank, for a lunch meeting, but want George and Harry to know you’re contacting Frank, you’d put their names and addresses in the CC line and they’ll get copies of the email you send to Frank.