Replying to private messages in laravel. Database structure

I am currently building a one to one private messaging system. I have one table in which I store the subject, message, receiver id, sender id, and unread. I want the users to be able to reply to the messages they receive. How should I approach this? Should I split the table? How should I structure it?

One more thing - how should I handle message deleting?

via Chebli Mohamed