When sending a newsletter, you need to hide the names and e-mail addresses of other people receiving that newsletter. My provider lets me send newsletters to 177 people and all of them cannot tell who else is receiving a copy of my newsletter. When you reveal the names and e-mail addresses of other recipients, then anybody receiving your newsletter could easily harvest the additional names to their contact list. Your contact list may be your most valuable asset. Don’t give it away.
From Escape the Cubicle