[Exim] $sender_helo_name with exim 2.x and system filter fil…

For some reason this does not seem to be getting the data given in a
HELO/EHLO, and one particular spammer uses the same string and I would
like to trash their mail via a system filter file, but it does not work
(as I would expect).
Thus I'm wondering what I'm missing... I've read and re-read the filter
doc.

Thanks.

-- 
Alan Thew                                       alan.thew@???
Computing Services,University of Liverpool      Fax: +44 151 794-4442