Put the addresses in the BCC (Blind Carbon Copy) field of the mail header.
If that field doesn't show while you're composing a E-mail go to the View
menu and select 'BCC Field'.

Signature
Russ Valentine
[MVP-Outlook]
>I want to send an email to several people but do not want
> each person knowing that this was also sent to other
> people. How do I suppress the sent to names?