reciepents

Guys when sending messages to group of our friends in gmail,yahoo mail or anything,all of them see the reciepents each other ,so is there any thing like ,no one sees the other reciepents except sender and reciever here ?

Hello friends, When i try to send an email to agent001 or some one othen than a message come to me that my message can't delivered because of intended reciepents. Please solve my problem.