Cc: header is one of a few that specify the list
of primary recipients. The sendmail program
treats the Cc: header no differently from the way
it treats the To: header. From the
user's point of view, the Cc:
header implies that there are recipients to whom an informational
copy of the message was supplied.
The Cc: header should never
be declared in the configuration file.
The field for the Cc: header must contain one or
more properly formed addresses, where multiple addresses must be
separated by commas.