Use BCC
blind carbon copy

There is a “cc:” field under the “to” field, but there is also be a “bcc:” field, which will send it to the recipients in that field without displaying the email addresses.

In Yahoo! this isn’t automatically displayed, but there is an option to “Show Bcc” at the top of the window pane.

Just put your own name in the “To” address, and everyone else in the “Bcc” field and everyone will get the email, but only see it was sent to you.