Just like people have a street address, people on the Internet have an e-mail address. An email address has at least four parts. The first part identifies the person. The left side is the user side of the address. And lastly there is the user's domain type.
Different countries use different systems.
There are no spaces between anything, just a dot between the last two parts. Then when you send an email to a friend, you just click on that email address and you do not have to copy it in. It is more convenient and accurate. In this case, the first person will see the cc and know that a copy was sent to a particular person. If you cannot, just send a note that you received it and give the date when you will answer it.