Hide recipient names by using Bcc
You can hide recipient names in your e-mail messages by listing them in the Bcc field. Bcc helps you keep people in the loop and respect their privacy by not disclosing their identities. For example, if you send a job announcement to multiple people, you may want to use Bcc to keep the identities of the potential job seekers private.
In your message, on the Options tab, click Bcc.
Type your recipients' names in the Bcc box.
Compose your message, and then on the Message tab, click Send.