I have an exchange 2010 server where I created a distribution group, added internal and external email addresses.
The intention was to allow a conversation between multiple users, sending an email to the DG would send the email to all participants, internal and external, then allow them to reply to the DG so that their reply was again forwarded to all members.
The problem I'm having is when an email is sent to the DG, it is sent to everyone in the DG but goes out with the originating senders email address, if any of the recipients reply, they reply to the original sender, not the distribution group. I looked at the transport rules, rewriting the senders email address appears that it would change all outbound emails for that person. This would interrupt their normal email exchanges so it's not (If I'm correct) not a workable option.