Tom kindly sent me the cure:

>X-Sieve: CMU Sieve 2.2
>From: "Carrington, Tom" <TCarrington@ReliTech.com>
>To: "'Andrew Grebneff '" <andrew.grebneff@stonebow.otago.ac.nz>,
>    "'vanagon@GERRY.VANAGON.COM '" <vanagon@GERRY.VANAGON.COM>
>Subject: RE: Listmom... "<Vanagon>" in message headings?
>Date: Fri, 20 Feb 2004 11:52:26 -0500
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>Hi Andrew,
>
>That is a user-configurable option, and the list has it set to "off" by
>default.
>
>If you would like to turn it on, send a e-mail to listserv@gerry.vanagon.com
>and in the message body, enter the words:
>
>set vanagon subj
>
>Once you do that, the messages will have the [Vanagon] prefix.
>
>Hope this helps!
>
>Your Vanagon List Admin,
>TomC