A question about messages and Sentbox vs Outbox

Hello. I don't know if this is the right place to ask this question, but I didn't know where else to post this.

What is the difference between the Outbox and Sentbox on Forumophilia? I tried to send a message but it's in the Outbox folder. Does that mean it was sent? If so, why is it not in the Sentbox folder?

Thank you for your time.

Hi

Your message has already been sent but has not been read yet.

Best wishes