I read somewhere on the Apple forums about this tip.

I wanted to configure my mail account from scratch, in Mavericks, sync the remote e-mails by IMAP and then import the local e-mails.

So, to get my old local On My Mac > Archive folder I

1. Quit Mail.app
2. Copied Archive.mbox from a backup to ~/Library/Mail/V2/Mailboxes
3. Deleted from ~/Library/Mail/V2/MailData the following items
   • Envelope Index
   • Envelope Index-shm
   • Envelope Index-wal
4. Relaunched Mail.app and proceed with the importing wizard
5. Renamed the newly imported folder to Archive (until renamed the e-mails show up as blank)

Here, Archive is just my example mbox, substitute with yours.

I read somewhere on the Apple forums about this tip.

I wanted to configure my mail account from scratch, in Mavericks, sync the remote e-mails by IMAP and then import the local e-mails. Since I forgot to use the export function in Mail, before installing Mavericks, I just copied the old local mbox over, but Mail wouldn't automatically pick it up, and using the import function on the same folder, simply didn't import anything.

So, to get my old local On My Mac > Archive folder I

1. Quit Mail.app
2. Copied Archive.mbox from a backup to ~/Library/Mail/V2/Mailboxes
3. Deleted from ~/Library/Mail/V2/MailData the following items
   • Envelope Index
   • Envelope Index-shm
   • Envelope Index-wal
4. Relaunched Mail.app and proceed with the importing wizard
5. Renamed the newly imported folder to Archive (until renamed the e-mails show up as blank)

Here, Archive is just my example mbox, substitute with yours.