Bccthis is a free addon for outlook which allows you to send a separate discreet message or private or secret message with outlook, this simple free plugin will help you send some important message about which the recipient had no idea. [ as shown in the snapshot below ]

This plugin allows the following functions and key features

Message Creation – Quickly create an additional message to one or more recipients of your e-mail. Format the e-mail any way you like for additional emphasis

Minimize Bccthis – Keep Bccthis minimized when not in use to save space.

Safety – The recipients you did not select to receive the Bccthis message receive a normal looking e-mail, with nothing indicating the sender sent Bccthis information to other recipients.

Protect Your Private Messages – When you try to Reply-To-All or Forward a Bccthis message, you are reminded about the private nature of the message and given an option to only send the public content.

Select Bccthis Recipients – Simply click "Select Recipients" and choose only those individuals you wish to send the Bccthis message to. Only those selected will receive your private message.

Download Bccthis plugin for outlook | You can optionally check out Bccthis for twitter and blackberry