[Stk] mbox archive file?

[Daniel]

I opened STK mbox archive in emacs using
C-u M-x rmail RET stk.mbox RET

BABYL OPTIONS: -*- rmail -*-
Version: 5
Labels:
Note: This is the header of an rmail file.
Note: If you are seeing it in rmail,
Note: it means the file has no messages in it.

What does that mean? 
Where are the messages?

Thanks,
Daniel