To send a message to multiple people such that each recipient cannot see the other recipient’s addresses or names; List their email addresses in the Bcc field (Blind Carbon Copy).

Outlook 2003
To display the Bcc field for use, enable it from the View menu in the Mail composition field in Outlook.

Outlook 2007
To display the Bcc field, Compose an email and select the Options Tab and the Show Bcc button.

Outlook 2010
To display the Bcc field, Compose an email and select the Options Tab and in the Show Fields category, select Bcc.