This post is going to focus on the use and deployment of a custom Group Policy to disable the Reply-All functionality in Outlook. The steps outlined below’ll effectively remove a user's ability to use the Reply-All functionality in Outlook via creation and deployment of a custom Group Policy Object (GPO). The examples presented below’ll target a dedicated Active Directory Organizational Unit. This OU will ultimately become the target for the deployment of the GPO as well as the container where user objects that have Reply-All removed will be homed in the Active Directory. That being said, the techniques presented here could be adapted to a broader environmental context based upon the discretion/desire of the administrator.

Full Article: Exchange blog