Good,
today I found an interesting extension for Microsoft Outlook: NoReplyAll AddIn. This addin, does the first thing you’re thinking: disable Reply To All, but that takes advantage of some own features of Exchange so that we may indicate in an email, we do not want that it can be answered with a “reply to all“.
For this we have a series of buttons on the Ribbon of an email, where we can configure who can not answer e-mail or that may not send the same.
This is much simpler than the use of DRM (which is recommended) and can be quite useful in certain scenarios.
I today already have used 2 times 
Greetings @ Home
The Bruno
HomePage: http://research.microsoft.com/en-us/projects/researchdesktop/noreplyall.aspx
Download: http://research.microsoft.com/en-us/downloads/60860f41-88ab-4bb4-8104-765feca9cfed/
El Bruno 