Carbon Copy – This field is usually used to enter addresses from which a reply would not normally be expected.
It is perfectly legitimate to populate the TO field with several addresses.
In common usage, TO field recipients are the primary audience of the message and CC recipients are others whom the sender wishes to publicly inform of the message.
The addresses entered in the CC field and revealed to all recipients. If this is not desirable, depending on the situation, an alternative field, BCC, is available for hidden notification.