I'm trying to achieve same thing as this. Here is how my DB desing look like:
So far, I have one page called mailbox.php, and template which should call PHP class and render view depending of action type using URL segments (new message, read new messages, read all messages...).
Now, I need some brainstorming: What I have to do? Create more pages? Use custom tables? Use repeaters for many-to-many relationships or just making fields?
I'm really stuck here and don't know what to do..