Mac OS X 10.4, Mail: Some mailbox files used by Mac OS X 10.3 are not deleted after importing

If you used Mail with Mac OS X 10.3, then upgraded to Mac OS X 10.4 Tiger and imported your Mail mailboxes (messages and attachments), please note that Tiger will not delete some previous mailbox files. Tiger keeps them around just in case you want to back up your Mac OS X 10.3 mailboxes.

This won't pose any issues with your current mailboxes. However, if your previous mailboxes are pretty big—maybe you have lots of attachments or large messages—you might enjoy the disk space you'd get back by deleting them.

If you want Tiger to "devour" those mailboxes to free up some disk, follow these steps:

1. In the Finder, choose Home from the Go menu.
2. Open the Library folder.
3. Open the Mail folder.
4. Open the Mailboxes folder.
5. If you want to back up (archive) the mailboxes before deleting them, copy them to a different location, such as a burnable disc.
6. Open, one at a time, the mailbox folders that end with ".mbox" or ".imapmbox". (If you're curious, these folders were actually package files in Mac OS X 10.3 Panther.)
7. Inside each ".mbox" or ".imapmbox" folder, you'll see some items. Do not delete every item you see. These are files you may safely delete if you want to free up some disk space:
   
   
   • mbox (which is a file, not a folder)
   • table_of_contents
   • mbox.SKindex
   • Info.plist (but not Info.plist that's in the Mailboxes folder)
   • mbox.SKindex.isValid
   • content_index
   • content_index-(your computer name)-Computer.local
   
   It's OK if you don't see all of those files in each folder.
8. Empty the Trash.

Important: Do not delete any folders, including ".mbox" folders, ".imapmbox" folders, or "Messages" folders." These are used by Mac OS X 10.4.

Tip: If you don't immediately see available disk space increase, you probably have FileVault home folder protection enabled—simply log out and back in to let FileVault recover disk space.