Interesting problem I got here. This is only happening to one person in the whole company so it doesnt appear to be a wide spread problem. Here is the problem.
One person in the company sends a lot of emails. When she makes an attachment to the email though the email gets to the recipient but instead of going to the Sent Items folder, the email is stripped of its content (To: From and the body, but not the attachment) and is left in the Outbox. It appears to also go to the Sent item folder completely whole. So the email that is sent is in two places... the Outbox and the Sent item folder. But the one in the Outbox is stripped of everything but the attachment. Strange eh?