Here's how you get your space back: My controls > under "Messenger" go to Archive Messages > Then in the drop boxes, put in your criteria for how many messages you want to archive > Press "Process" and you'll get an e-mail containing all of your PM's in 1 file and your space in your Inbox will be back. Hope I helped.
Go into your private messages folder, go down to the lower left corner, and where it says "Quick Clicks," click the drop down arrow, and go to Sent Items. You probably have stuff there, just delete it.