I can't get my Sent folder to sync with the IMAP server. I've had this issue back when I had Snow Leopard too. In the picture, the top sent is local, while bottom is server. Whenever I send emails, half the time they don't get delivered, and if I open the email account through web (I use web hosting+domain for email), then its sent folder isn't updated with the latest sent email from Mail either. I've checked server settings several times, and everything seems ok on that part. It worked correctly when I used Windows with Outlook Express.