I believe the Client Newsletter list of people is drawn from your leads and clients that you have in your IDEA database already.
So, go to Clients and Leads on the left hand side of your Profile home page. Then scroll over to +Add Contacts–you should be able to enter the name and e-mail information together. (I’m not sure there is a way to do this under the Manage Client Newsletter option as I can only see the enter e-mail option).
Hope this helps! If not, perhaps someone from IDEA will respond.