If you are an Outlook user and looking for a feature to disable reply all option the NoReplyAll plugin from Microsoft Research is for the rescue. It is a small plugin, when installed add two new buttons No Reply All and No Forward to the new message UI as shown below
The buttons are self explanatory and use them whenever required for your email.
Download NoReplyAll Outlook Add-In From here which is just 300 KB in size. It is a zip file and when extracted will have 4 files including setup.exe and 1 folder in it.
Double click setup.exe to start the installation
It would ask for confirmation to install the tool and once confirmed it would continue with the installation
When the installation is complete just click close to on the popup.
Now NoReplyAll Addin for your Outlook is ready for use.
Note: This plugin works only with mailing systems that use Microsoft Exchange Server as the backend and will not work for users using web based email like gmail.
In short it is a very handy tool for a Outlook 2007 and 2010 User.