Last month I wrote about a handy plugin developed by Microsoft Research that would prevent someone from replying to all on an email that you originated. Well that plugin has been updated and the newest version is now available for download from the Microsoft Research site.
The primary function of this add-in is to 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.
So not only does this plugin take care of the Reply to All piece but it will also check if you left the subject line blank or forgot an attachment. Sounds like the trifecta of typical email errors to me and a way to keep them from happening.