I can no longer create or delete a folder ("mailbox") in Mail. I have tried going through the mailbox menu, using the + at the bottom, and cntrl clicking, but when I click on "New Mailbox" nothing happens. It doesn't work under "on my mac" or the specific accounts. Everything is updated & I have restarted both mail and my MBP. I have googled it to death, but no one else seems to have had this problem. Any guesses?? Thanks!