Smart mailbox can't be deleted ands new ones disappear!!!
There's a solution offered for this problem on here but it's incorrect. There is no "Delete Smart Mailbox" option under the Mailbox drop-down menu.
I set up a smart mailbox a few years ago and don't need it any more. So I tried to delete it and it just keeps coming back every time Apple Mail launches. So annoying. What's even worse is that if I create an additional new one that one disappears next time the app launches. Editing the zombie one that doesn't work either. It reverts back to the original settings on relaunch.
MacBook Air