Prevent people from replying to all the recipients. NoReplyAll Outlook Add-In add a couple of buttons to the Outlook ribbon to prevent people from replying to all the recipients of your message or forwarding it.
The add-in uses a facility built into Outlook and Exchange that is more lightweight than information-rights management but is not exposed in the existing UI. The add-in also includes a check for common email errors, such as omitting attachments or subject lines.

Requirements:
* Outlook 2007 and 2010

The license of this software is Freeware, you can free download and free use this outlook add-ons software.