On 30 Mar 2005 at 15:27, Matthew Lenz wrote:

<snip>
 
> here is an example of the headers from an spam that wasn't caught

> X-Spam-Status: No, score=4.1 required=5.0 tests=BAYES_99,HTML_80_90,
>         HTML_FONT_BIG,HTML_MESSAGE,HTML_TITLE_EMPTY,MIME_HTML_ONLY,
>         MSGID_FROM_MTA_ID autolearn=no version=3.0.2

> Ideas where to start (other than having her change her email address
> hehe)

The first thing I did upon installing SA 3.x and running it for a few 
days was to restore some sanity to the BAYES_* scores.

The GA has a tendency to tune down the scores assigned for extreme 
bayes results because they tend to cluster with other positive tests 
(like SURBLs).

That has the unfortunate side effect that when a message comes 
through which for whatever reason fails to trigger much besides 
BAYES_99 (as your example false-positive did), then the assigned 
score will be lower than it should be if you trust bayes, which you 
should be *more* inclined to do for the extreme cases than not.

The default 3.x scores are as follows:

score BAYES_00 0 0 -1.665 -2.599
score BAYES_05 0 0 -0.925 -0.413
score BAYES_20 0 0 -0.730 -1.951
score BAYES_40 0 0 -0.276 -1.096
score BAYES_50 0 0 1.567 0.001
score BAYES_60 0 0 3.515 0.372
score BAYES_80 0 0 3.608 2.087
score BAYES_95 0 0 3.514 2.063
score BAYES_99 0 0 4.070 1.886

Notice that for the fourth column (bayes + network tests enabled) 
BAYES_99 actually scores *lower* than BAYES_80!

I've added the following lines into my local spamassassin 
configuration, based on the scores from SA 2.6x and my own 
experience:

score        BAYES_00 0 0 -4.901 -4.900
score        BAYES_05 0 0 -0.925 -2.599
score        BAYES_20 0 0 -0.730 -1.951
score        BAYES_40 0 0 -0.276 -1.096
score        BAYES_50 0 0 1.567 0.001
score        BAYES_60 0 0 3.515 1.592
score        BAYES_80 0 0 3.608 2.087
score        BAYES_95 0 0 3.514 3.514
score        BAYES_99 0 0 4.070 5.400

Making this single change would have caught your sample false 
positive based solely on the BAYES_99 result.

----
Nels Lindquist <*>
Information Systems Manager
Morningstar Air Express Inc.

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