set prompt-for-cc

SET PROMPT-FOR-CC YES/no  -  whether to prompt for a CC

With the usual YES setting, MM prompts for a CC during the send routine.  
  (You are normally prompted for TO, CC, SUBJECT and MESSAGE if you do not
  put an address on the command line with SEND.)

If you change it to NO, a prompt for CC will not appear.  You can insert
  a CC field by using the CC command at the Send> prompt.

For more help, type "help" and one of the following:
(at any prompt:)  save-init   set   show   set prompt-for-bcc
(at the Send> prompt:)  cc
(at the MM> or Read> prompts:)  send