Mail.app -- Sent Emails NOT Saved

Please see this screenshot: http://geoffmyers.net/images/mail_screenshot.png

Since August 20, none of my sent emails have been saved by Mail (the account is IMAP). If you see the screenshot, you can see that, for some strange reason, Mail shows several subfolders under Sent instead of just a single folder (like my other 2 email accounts on the bottom). This only began recently. I can access all my Sent emails sent before August 20 within the "Sent Messages" folder. But now I think Mail is confused as to where sent emails go, so it doesn't save them. Please advise. Thank you.

 

Thank you so much! I had completely forgotten about that feature of Mail.