[Dovecot] help writeing rule for preventin spam

[Sophia Alikhani]

I used dovecot-1.1.7 + qmail-jms1-7+ vpopmail + ...
everyday , everyuser has many spams from his/her mail to his/her for
example in Bulk folder there are many spam e-mails that the sender is
ourselves (from mymail at mydomain to myself at mydomain)
how can i prevent these types of spam

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with regards
Sophia Alikhani
WorkPhone: +98-21-8497057
Mobile : +98-912-3361036