Is it proper to use Cc:, CC: or cc: for copies in a business letter. Thanks, S. Peoples
If you look here, you'll see that different dictionaries use different forms:
cc - OneLook Dictionary Search
The more conservative ones like Oxford use lower case and don't give 'carbon copy' for the upper case abbreviation. There isn't much logic behind 'Cc', but it is widely seen in email. I use 'cc', but can't see much wrong with upper case version.