table
ofcontents 56K
mbox 11.5 MB
Info.plist 4 K
content_index 3.1 MB
Your inbox must have the extension .mbox.
Check that with getinfo in the finder (from file menu) and check also that "hide extension" is not active, if the extension is not present you could add .mbox.
than return to mail and see what happen.
If you couldn't see the mail do that inside the mail.app:
Select your mailbox and go to menu mailbox->Rebuild in your mail.app.
bye
fede