You can hide recipient names and addresses in your email messages by using Bcc, which stands for "blind carbon copy." Bcc helps you keep people in the loop and respect their privacy by not disclosing their identities. When you send an email message, your recipients can see the addresses in the To and Cc fields, but not the Bcc field.
Add a recipient to the Bcc field
In your email message, click the Options tab > BCC.
Type the recipient's name or email address in the Bcc field.
NOTE: The Bcc field isn't currently available for meeting requests.