[CentOS] Unknown mail transport error

Wed Aug 20 11:50:18 UTC 2008
Anne Wilson <cannewilson at googlemail.com>

I've just signed a bunch of keys using the caff tools.  A few minutes ago they 
started bouncing back at me, with the above error.

Received: by anne-wireless.lydgate.net (Postfix, from userid 500)
        id CA4B230EF7; Wed, 20 Aug 2008 11:15:39 +0100 (BST)
MIME-Version: 1.0
Subject: Your signed PGP key 0x2C4F325BFF906D62
User-Agent: caff - http://pgp-tools.alioth.debian.org/
X-Mailer: MIME-tools 5.425 (Entity 5.425)
Sender: anne <anne at anne-wireless.lydgate.net>
Content-Type: multipart/encrypted;

I used the same tools last year without problems, but obviously something is 
different this year.  Can anyone suggest what's wrong, and what I can do 
about it?

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