TIP As of the new version of Apple’s Mail, you can now rearrange the sidebar folders – Mailboxes, On My Mac, Reminders, Smart Mailboxes, and so on. Just click and hold on any folder and then drag the folder to a new position. You don’t even have to have Mailboxes at the top of the list. You’ll like this news if you have a lot of IMAP accounts, because each clutters the sidebar with a needless folder. While you can’t rid the sidebar of those folders, you can at least move the more important On My Mac folder above them, making it easier to file email messages via drag and drop.
You can also delete folders you’re not using. To get rid of Mail’s RSS folder, for example, open it, hold down shift, and click on each feed in the list. Control-click on the selection and choose Delete Feeds from the contextual menu that appears. When you’ve deleted all the feeds, the RSS folder in the sidebar icon will also vanish.
You can manually delete a stubborn draft in Apple’s Mail if you know where to find the file