Negative spam score evaluated to positive.

Hi everyone..
  First post to this list and recent production server Vexim user.  Wondering if anyone has had any issues with 
negative spam scores being evaluated positive?  Here is the /var/log/maillog entry:

Aug 30 11:33:42 mail spamd[21633]: spamd: checking message 
<[email protected]> for mailnull:26
Aug 30 11:33:44 mail spamd[21633]: spamd: result: . -2 - BAYES_00,HTML_MESSAGE 
scantime=2.0,size=3484,user=mailnull,uid=26,required_score=5.0,rhost=localhost,raddr=127.0.0.1,rport=49548,mid=<B160ACF
[email protected]>,bayes=0.000000,autolearn=ham

  And here is the portions of the message headers my users forwarded me:

> ***** Start of Included E-mail ***** 
> Authentication-Results: domain.net 
>          [email protected]; domainkeys=neutral (no sig) 
> Subject: Please call me 
> Date: Sat, 30 Aug 2008 11:33:17 -0700 
> X-MS-Has-Attach: 
> X-MS-TNEF-Correlator: 
> Thread-Topic: Please call me 
> thread-index: AckKzt9JChe3MWf/QbyZBG76ujzb4A== 
> From: "Sender" <[email protected]> 
> To: "Receiver" <[email protected]> 
> X-Outbound-IP: 1.2.3.4 
> X-Env-From: [email protected] 
> X-Virus-Status: Scanned by VirusSMART (c) 
> X-BTI-AntiSpam: 
> score:50,sta:off,dcc:off,dnsbl:passed,sw:off,bsn:30/passed,spf:off,dk:passed,pbmf:none,ipr:0/1,trusted:no, 
> ts:no,bs:no,ubl:off 
> 
> X-Spam-Score: -2.6 (--) 
> X-Spam-Report: Spam detection software, running on the system 
> "receiverdomain.net", has 
>          identified this incoming email as possible spam.  The original 
> message 
>          has been attached to this so you can view it (if it isn't spam) or 
> label 
>          similar future email.  If you have any questions, see 
>          The administrator of that system for details. 
>          Content preview:  Omitted [...] 
>          Content analysis details:   (-2.6 points, 5.0 required) 
>          pts rule name              description 
>          ---- ---------------------- 
> -------------------------------------------------- 
>          -2.6 BAYES_00               BODY: Bayesian spam probability is 0 
> to 1% 
>          [score: 0.0000] 
>          0.0 HTML_MESSAGE           BODY: HTML included in message 
> 
> Omitted
> ***** End of Included E-mail ***** 

  Thanks in advance if anyone has any suggestions.

--
Colin Dick
OCIS Admin