'No mails to output'?

From: Charles Johnson <cj_at_cehjohnson.uklinux.net_at_hypermail-project.org>
Date: Mon, 22 Aug 2005 19:17:21 +0100
Message-ID: <430A16B1.7070805_at_cehjohnson.uklinux.net>

charles_at_airemail:/home/smbs/common/hypermail/in$ hypermail -p -m Inbox -d ../out

Loading mailbox "Inbox"...
  0 messages.
Writing messages to "../out/"...
No mails to output!

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"No mails to output!" yet 'Inbox' is a sizeable mail file from Thunderbird. Am i doing something stupid with the above command? Received on Tue 23 Aug 2005 01:28:14 AM GMT