How do I find my OUTBOX for sent messages?
First you need to have message saved that you sent. You can click the save message box before sending the message or you can go to profile>modify profile>personal messaging and check the box to save all messages. As a moderator I save all message should an issue occurs where I need to product the original but most people never check the option.
Once you have accumulate message, my message>messages>sent item will allow you to view the messages after you have sent them.