spam that only hits the BAYES_99 rule

[Tom H]

Hi,

I was getting hit by a great deal of spam that only hits the BAYES_99
rule, and maybe gets less than a point or so from elsewhere.
But now I'm getting ones through that are basically only hitting the
BAYES_99 and nothing else;
X-Spam-Score: 3.5 (***) BAYES_99

I tried to send the mail to this list to demonstrate the content but got 
bounced with 12.9 spam score.

I'm running sa-update weekly, and rules_de_jour daily with a big set of 
rules, and I'm still not hitting loads of obvious spam. Particularly 
those with the title "Re:" + "good" and then a number appended to the end.

The only thing I can think of at the moment is to reduce my 
requried_hits to 3.5 or increase the score for BAYES_99 to 5, but I 
would prefer not to do the latter as I like a default and automatically 
updated installation.

I would be grateful for any ideas on this...

Thanks,

Tom H