understand "to:", "cc:" and "bcc:" fields

the "to:" field contains addresses of people to whom you are directly talking.

the "cc:" (carbon copy) field contains addresses of people who you feel should also be hearing the conversation, but are perhaps not expected to respond, not that they are precluded from doing so.

the "bcc:" (blind carbon copy) field contains addresses of people who you feel should also be included in the conversation.  however these addresses will be hidden from all other recipients of the message.  other recipients will be unaware of, and unable to respond to, people listed in "bcc:" field.

a fine use of the "bcc:" field is the birth announcement to 200 people.  if one of the recipients unwittingly hits the "reply all" button, all 200 will not receive the congratulatory response.