How does one transfer a mailbox in mail 5.3 (OS 10.7.5) to an older computer (OS 10.4.11) running mail 2.1.3. Exporting from mail 5.3 and importing into mail 2.1.3 gets the message "no proper OS X mailboxes found". Directly transferring the mailbox folder into the user/Library/Mail spot results in the mailbox name appearing, but no messages. The file itself is like 100 Mb. The data is there but the old program can't recognize it. Is there any way to recover from this situation?