threaded

Having threads.

Of messages: arranged in a thread or threads.

A threaded email will commonly have a number, (e.g., (5)) after the sender's name to show how many emails are in that thread. An unthreaded email, however, will not have that number marker because all the messages are listed separately.

Of messages in a digital forum conversation: displayed hierarchically (based on parent messages), rather than linearly (usually purely chronologically).