Due to various and persisting problems, I had to reinstall 10.8.2.

What I did

  • Shut down iMac with internal system disc A.
  • Started 10.8.2 recovery system
  • Copied iMac's system disc A to an external disc B as an image using Disc Util
  • Erased system disc A as HFS / journaled
  • Run a clean install on A

Then, I told OS X Mail to import old mailboxes from B into the fresh Mail system.

Ugly result

Unfortunately, I got tons of tons of deeply nested folders, which eventually contain email:

                            <this folder finally contains some emails>

Not hardly to see, I can't use these imported folder structure any more.


Is anybody aware of a tool to fix such problems?

  • 1
    There's a Rebuild Mailbox menu item in Mail.app. Does that help? Mar 10, 2013 at 2:09
  • Did that with various folders. The ugly structure persists.
    – SteAp
    Mar 10, 2013 at 2:11
  • Restore from Time Machine backup? Mar 10, 2013 at 2:20
  • What should I restore? The contents of ~/Library/Mail/
    – SteAp
    Mar 10, 2013 at 2:23
  • 2
    What problem are you trying to solve? Do the messages appear correctly in Mail?
    – bneely
    Mar 10, 2013 at 4:05

2 Answers 2


That "ugly" result is not a corruption or mistake, it's the way the Mail folder is structured now.

If you've been messing with its contents, I'd suggest emptying ~/Library/Mail/V2 and starting over again from your original source, re-importing or using Migration Assistant.

No, I don't know why either.

  • The reason is an often used one, to limit the number of files in a directory so to give faster access. Unix has always used its file system for storing lots of small files rather than put the data in a database as you tend to on other OS
    – mmmmmm
    Mar 11, 2013 at 9:50
  • I didn't know that, and it was a pretty big surprise this long-time users, don't blame others for being confused! Thanks!
    – Zo219
    Mar 13, 2013 at 0:41

Actually, I believe what Apple does is create a folder structure of their own and encapsulate it in a .mbox file; it doesn't adhere to the mbox standard though. See screenshot 1, this is inside "Receipts.mbox": enter image description here

What I did was import the .mbox files one layer deep. This is tricky because the Import dialog won't let you go "into" a .mbox "file" (which is actually a directory in this case); you have to navigate into the folder from the finder and then drag it to the import box to force the dialog to go there. Alternately you can use the "Go" command with cmd+shift+g: enter image description here

And then when it seemed to come into my mail cleanly, enter image description here

I re-exported it and found that this was the result, which I think is adhering to the mbox standard. See how the emails are now concatenated into the .mbox file, as opposed to stored in folders and then eventually as .emlx files with the attachments being separate? Re-importing them on the original machine this way yielded good results.

enter image description here

Note that this was all on macOS Sierra 10.12.1.

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