I have configured Mail.app to move deleted messages to the Trash mailbox and to store deleted messages on the server. Under the .Mac tab in the mailboxes list on the left-hand side of Mail.app, I see a folder called "Deleted Messages". There's nothing in it. But I've tried deleting this folder, and it continues to reappear. All of my deleted messages are in the Trash mailbox, so I'm not sure what this one is for.