could we add a rule that gives a negative score when the mail client is 
detected as being Lotus Notes ? Lotus Notes is a common tool within companies 
but not used as a bulk mailer.

Sample X-Mail headers from a grep in our company's data:

X-Mailer: Lotus Notes Edition France 5.0.2c 8 =?iso-8859-1?Q?f=E9vrier_2000?=
X-Mailer: Lotus Notes Edition France 5.0.2c 8 =?iso-8859-2?q?f=E9vrier_2000?=
X-Mailer: Lotus Notes Release 5.0.10  March 22, 2002
X-Mailer: Lotus Notes Release 5.0.11   July 24, 2002
X-Mailer: Lotus Notes Release 5.0.11  July 24, 2002
X-Mailer: Lotus Notes Release 5.0.2a  November 23, 1999
X-Mailer: Lotus Notes Release 5.0.2b (Intl) 16 December 1999
X-Mailer: Lotus Notes Release 5.0.2c (Intl) 2 February 2000
X-Mailer: Lotus Notes Release 5.0.2c (Intl)8 Fevereiro 2000
X-Mailer: Lotus Notes Release 5.0.3 (Intl) 21 March 2000
X-Mailer: Lotus Notes Release 5.0.3 14 April 2000
X-Mailer: Lotus Notes Release 5.0.4  June 8, 2000
X-Mailer: Lotus Notes Release 5.0.4a  July 24, 2000
X-Mailer: Lotus Notes Release 5.0.5  September 22, 2000
X-Mailer: Lotus Notes Release 5.0.6  December 14, 2000
X-Mailer: Lotus Notes Release 5.0.6a  Janeiro 17, 2001
X-Mailer: Lotus Notes Release 5.0.6a  January 17, 2001
X-Mailer: Lotus Notes Release 5.0.7  March 21, 2001
X-Mailer: Lotus Notes Release 5.0.8  June 18, 2001
X-Mailer: Lotus Notes Release 5.0.9  November 16, 2001
X-Mailer: Lotus Notes Release 5.0.9a  January 7, 2002
X-Mailer: Lotus Notes Release 5.0.9a  Janvier 7, 2002
X-Mailer: Lotus Notes Release 5.07a  May 14, 2001
X-Mailer: Lotus Notes Release 5.0a (Intl) 4 May 1999
X-Mailer: Lotus Notes Release 6.0 September 26, 2002
X-Mailer: Lotus Notes Release 6.0.1 February 07, 2003
X-Mailer: Lotus Notes Version 5.0.2c (Esp.) 8 febrero del 2000
X-Mailer: Lotus Notes Version 5.0.2c (Intl) 08 Februar 2000
X-Mailer: Lotus Notes Wersja 5.0.3 (Intl) 21 marca 2000
X-Mailer: Lotus Notes Wydanie 5.07a  14 marca 2001
X-Mailer: Lotus Notes ÷ÙÐÕÓË 5.0.9a  7.01.2002

Sample Lotus Notes email (addresses obscured):

From xxxxx@xxxxxx  Thu Feb 27 15:28:59 2003
Received: from xxxxxxxx (unknown [194.35.153.107])
        by xxxxxxxxxx (Postfix) with ESMTP id 2A4E31C31E7
        for <xxxxxxx@xxxxxxxx>; Thu, 27 Feb 2003 15:28:59 +0000 (GMT)
Received: from mail.arthurfrance.com (unverified) by xxxxxxx
 (Content Technologies SMTPRS 4.2.10) with SMTP id 
<T60ac4ebbbdc223996b8ec@xxxxxxxxxxx> for <xxxxxxxxx@xxxxxxx
m>;
 Thu, 27 Feb 2003 15:28:21 +0000
Received: from parfw4002 [192.168.200.202] by mail.arthurfrance.com
  (SMTPD32-7.13) id A0CF22900F8; Thu, 27 Feb 2003 16:37:51 +0100
Received: from plald2001.arthurfrance.com ([10.104.72.8]) by parfw4002; Thu, 27 
Feb 2003  +0100 (Romance Standard Time)
Subject: Re: Alors on fait la carpe ?
Importance: Normal
Sensitivity:
X-Priority:
To: xxxxx@xxxxxxx
Cc: "xxxxxx" <xxxxxxx@xxxxxxxx>,
        "xxxx" <xxxxx@xxxxxxxx>
X-Mailer: Lotus Notes Release 5.0.5  September 22, 2000
Message-ID: <OF07904B2E.8F66301C-ONC1256CDA.005486A5@arthurfrance.com>
From: xxxxx@xxxxxx
Date: Thu, 27 Feb 2003 16:24:23 +0100
X-MIMETrack: Serialize by Router on PLALD2001/Server/ArthurFrance(Release 
5.0.10 |March
 22, 2002) at 27/02/2003 16:23:19
MIME-Version: 1.0
Content-type: text/plain; charset=iso-8859-1
Content-transfer-encoding: quoted-printable

email text is here