When setting up a new Leopard machine, I couldn't get any of my sub-mailboxes to show up under the mailboxes as they were on my other machines. The trick to fix this was to go into the Advanced tab of the settings for each IMAP mail account in Mail's preferences, and remove the IMAP path that's now defaulting to INBOX. When you remove this entry, Mail finds the rest of the mailboxes, and puts them back where they have always been, under the inbox for each account. While there are similar hints related mostly to Gmail, this particular issue doesn't seem to be covered by any existing hints. [robg adds: I've not seen this issue myself, but I migrated my Mail accounts from my prior system. If you can confirm (or contradict) please post in the comments.]

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