use cc for all the addresses

everyone that you put in the "to" or "cc" lines will be seen by everyone you send the email to you need to use the "bcc" line for the addresses that you dont want every one to see, it stands for blind carbon copy. most email programs dont have it turned on by default but if you go in the options you can turn it on and I will add how to turn it on in outlook here in a second

in outlook when you hit the to button in your email your address book comes up and you can add whoever you want to the to list, cc list, or bcc list

in yahoo mail you hit compose and at the top it asks if you want to add cc or bcc click on it and then you can add addresses in them