Is it possible to setup a DL which "all" users can send emails to, but recipients don't have permissions to reply to all or forward, they can only reply to the originating sender? E.g. For that particular message the reply to all and forward buttons are greyed out in Outlook. I know you can setup an Outlook Form for this purpose, but is there anyway it can be automated in AD/Exchange?

If you are granting all users the right to send to the DL, then all users will be able to reply, a reply is the same thing in theory. The only built-in rules you will get are set in active directory on the Exchange General tab of the DL. You may be able to acomplish this with rights managment for exchange.