a) 1 Mail id will be created which is linked to all 255 or more email id (Like yahoo group email id)
b) Any person in group, if drops email to this group email id,then email should be sent to all member of group linked to this group id...and taking the subject of this email ... automatically one discussion forum topic should be created.
c) If any member, changes subject and sends email, then it needs to be considered as 2nd topic