Thankyou Jacob ... this is very helpful.  It even includes
   [concealed]

for concealed subscribers (and I'd suspect anyone who set this up is concealed).
--Joe
________________________________________
From: LISTSERV list owners' forum [[log in to unmask]] on behalf of Jacob Haller [[log in to unmask]]
Sent: Monday, October 04, 2010 1:42 PM
To: [log in to unmask]
Subject: Re: Spam autoresponder-- finding a needle in a haystack

>that is nasty.
>
>I'd suspect this is being forwarded to the autoresponder, probably
>filtering for mail from your listserver (maybe specifically the list)
>
>check recent subscribers:
>   review _mylist_ (by date
>
>unfortunately, review will not display subscribers who have conceal turned on.

If you're the listowner or a site admin you can use

        review _mylist (by date all

and concealed subscribers will also be listed.