still problem in spam management

Hi everyone

I use bogfilter since months now, and I still have a problem of classification 
between ham and spam.
Half of my spam is still classified as ham.

Description of the system :
My bogofilter work on my mail server, the mail is delivered by postfix, 
bogofilter read it, rank it, mark it as spam or not ( ___SPAM___ in header) and 
make auto-update, and give it to postix again.
Postfix give it to dovecot deliver which set it in the corresponding box on 
imap. If marked as spam, they go in INBOX.spam...

After that, if I receive spam in my normal boxes, I put it in the spam box.

End of process : each day, a script read the messages in INBOX.spam and learn 
those without ___SPAM___ (so, the mistaken) to be real spam. The contrary to 
the rare ham that were in the spam box.
This script also run bogoutil -l wordlist.db and such things after having 
corrected the mistakes ...

Unless all this sophisticated process, half of my spam has still a bogofilter 
score of around 0.42, close to be considered really as spam, but not crossing 
the border !

Did I make a mistake somewhere ? what is the problem ?
Thank you
-- 
Stéphane Guedon
page web : http://www.22decembre.eu/
carte de visite : http://www.22decembre.eu/downloads/Stephane-Guedon.vcf
clé publique gpg : http://www.22decembre.eu/downloads/Stephane-Guedon.asc

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