[exim] Anti Asia Spam in system-filter

Hi,

I define in my system-filter:

# Asia Spam

if $header_content_type: contains "GB2312"
then
   mail to $return_path
        subject "Mail rejected, japanese or chinese content"
        file /usr/exim/tmpl/asiaspam-reject.txt
   seen finish
endif

If i test it with Content-Type: GB2312 it works.

But follow spam will reach me:

From: "!China Source" <98765@???>
Subject: 18:04:22Chinese
=?GB2312?B?U3VwcGxpZXJzo7rE+s/rs/a/2rL6xre1vbCiwK2yrrn6vNLC8KO/?=
To: fs@???
Content-Type: text/plain;charset="GB2312"
Reply-To: 98765@???

Does $header_content_type dont contains the complete string ? Any
ideas ?

Frank
--
Frank Simon                          ECCE TERRAM Internet Services GmbH
Tel. 0441 / 500 120                  Edewechter Landstr. 42
Fax. 0441 / 500 1229                 D-26131 Oldenburg
Ex Astris Scientia