To assign a user Read-Only access to a mailbox from Exchange is not very intuitive… But it’s not difficult by any means.
At RANDA, like many other organizations, we experienced the dreaded flurry of “Reply All” emails after someone sent an email to a Distribution Group that contained all users. We did not want to restrict access to the distribution group, but needed a solution to stop the onslaught of “Thanks”, “Awesome”, “Insert crude joke here”, etc.
To that end, we implemented a couple of Transport Rules that would strip out the distribution group from the To and CC field and add it to the BCC field. This created a system that would allow Reply All on other groups, but eliminate it on the company wide group. If the user clicks Reply All, the reply only goes to the originating user!