I gave it a whirl ... my laptop fan spun all the way up, noisy, long wait ... and it mostly worked! Mostly means that the Mail.app badge in the Dock showed the correct number of unread messages, but I was no longer seeing any messages in any of my Exchange (ewww) mailboxes. Oops! I deleted and re-created the account to get everything working again.
- Quit Mail if it’s open.
- In ~/Library/Mail/V2/MailData, delete any file that begins with “Envelope Index,” such as Envelope Index or Envelope Index-shm.
- Your home Library folder is hidden by default. To display it, choose Finder > “Go to Folder” and then enter “~/Library.”
- Open Mail.
- Mail creates new Envelope Index files. This process may take a few minutes, depending on how many messages Mail is reindexing.
I think my Mac is jealous of my Xubuntu laptop, so it's trying to tie up more of my time. I think that's gonna backfire ...