It's pretty much the last feature that is still missing since you forked Kopano.
The idea: users receiving mails through a (distribution) group should also be able to be permitted sending mails on behalf of the group -- so the group receives the direct response again. Many people still won't use Reply All in their mail client so their response won't go to the distribution group -- therefore my suggestion adding a Send As permission for groups as well.
Thank you for your time and consideration. 