Models for simple messaging system

I’m currently developing a community website that is to includes a
simple messaging system: Users can send email-like messages (sender,
recipient, subject, body, read-date, etc.) to each other. They have an
inbox and a sent box each. They can read and delete messages.

That seems to be straight forward, but I’m not so sure about the
requirements to come.

Are there some good examples how the model and DB schema could look