https://issues.apache.org/SpamAssassin/show_bug.cgi?id=6389

--- Comment #5 from [email protected] 2010-04-07 06:20:44 UTC ---
(In reply to comment #4)
> Regarding comment 0 and its sample FP attachment 4721 [details], it looks 
> like that
> should have been ALL_TRUSTED (see the documentation for internal_networks). 
> While this doesn't solve the bug, it would help alleviate the
> spammy-messages-from-colleagues problem.
> 
> Hm.  This header from attachment 4730 [details] is quite interesting:
> 
> X-MIME-Autoconverted: from quoted-printable to 8bit by popo.ctimail.com id
> o31FCcI16161
> 
> I believe this is reporting that ctimail's mail system converted the
> quoted-printable headers to 8bit, which triggered the rule.  Plugging that
> header into google shows 19k hits, which is small but not intangible.  Even my
> own sendmail server has added it in the past.  Comparative data: X-Spam-Status
> (236k), X--MailScanner (10k), X-Spam-Flag (27k), X-Greylist (17k), X-X-Sender
> (9k), X-Sieve (7k), X-Received (16k) ... (searches performed in quotes with a
> second query being "Message-ID" to ensure we're looking at email headers).
> 
> I've placed a possible fix into our QA system (20_bug_6389.cf in my sandbox) 
> to
> sanity-check it, containing the following code (the first rule is just a
> popularity test for that header):
> 
> header __HAS_XMIME_AUTOCONV     exists:X-MIME-Autoconverted
> header __MIME_QP_TO_8BIT X-MIME-Autoconverted =~ /from quoted-printable to
> 8bit/
> meta DOS_HIGHBIT_HDRS_BODY_BUG6389 __FROM_NEEDS_MIME && __SUBJECT_ENCODED_B64
> && __FROM_ENCODED_B64 && __SUBJECT_NEEDS_MIME && __HIGHBITS &&
> !__MIME_QP_TO_8BIT
> 
> Sadly, this doesn't help the first sample. Appending "&& !__RCVD_VIA_APNIC_LE"
> would also fail to solve it since it is from France and not Asia. According to
> yesterday's numbers, that extra requirement would also reduce the spam hit by
> 43% and the ham by under 20%, reducing 1.1268% spam to 0.7423% and the ham to
> somewhere between 0.0261% and the current 0.0326%.
> 
> I'm disheartened by the French FP as it was composed with the latest version 
> of
> Thunderbird (3.0.4, WinXP, French build), but at least configuring
> internal_networks would solve it for that particular user's internal company
> mail.  For a full fix, I can think of nothing but removing this rule.  The
> question becomes:  how many FPs does this rule really create, i.e. is this an
> isolated incident?


According to my email sample (attachment 4730), the email is scanned by
SpamAssassin before QP-to-8bit conversion (note the mail id o31FCcI16161)

Received: from smtp1o.ctimail.com (smtp1 [203.186.94.57])
    by popo.ctimail.com (8.11.1/8.11.1) with ESMTP id o31FCcI16161
    for <[email protected]>; Thu, 1 Apr 2010 23:12:38 +0800 (CST)
Received: from iguard1-206.hkbn.net (iguard1-206.hkbn.net [203.186.220.206])
    by smtp1o.ctimail.com (8.12.11/8.12.11) with ESMTP id o31FCalG014728
    for <[email protected]>; Thu, 1 Apr 2010 23:12:38 +0800 (HKT)
Received: from violet.alumni.cuhk.net ([202.45.188.23])
  by iguard1.hkbn.net with ESMTP; 01 Apr 2010 23:12:37 +0800
Received: from asavgw1.alumni.cuhk.net (asavgw1.alumni.cuhk.net
[202.45.188.44])
    by violet.alumni.cuhk.net (8.14.3/8.14.3) with ESMTP id o31FCUvr000701
    for <[email protected]>; Thu, 1 Apr 2010 23:12:31 +0800
Received: from ieaa.ie.cuhk.edu.hk ([137.189.97.6])
  by asavgw1.alumni.cuhk.net with ESMTP; 01 Apr 2010 23:12:36 +0800
Received: from smtp.ctimail.com ([203.186.94.58] helo=smtpo.ctimail.com)
    by ieaa.ie.cuhk.edu.hk with esmtp (Exim 4.63)
    (envelope-from <[email protected]>)
    id 1NxM4R-0006GD-8l
    for [email protected]; Thu, 01 Apr 2010 23:12:36 +0800
Received: from [127.0.0.1] (119247234247.ctinets.com [119.247.234.247])
    by smtpo.ctimail.com (8.12.11/8.12.11) with ESMTP id o31FCROw020860
    for <[email protected]>; Thu, 1 Apr 2010 23:12:27 +0800 (HKT)
X-MIME-Autoconverted: from quoted-printable to 8bit by popo.ctimail.com id
o31FCcI16161

I would say, the real bug should be in 20_html_tests.cf, which says

body __HIGHBITS                     /(?:[\x80-\xff].?){4}/

I think it should be 
rawbody __HIGHBITS                     /(?:[\x80-\xff].?){4}/

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