[Dovecot] help on writing a rule for perventing spam

[Sophia Alikhani]

Hi
I used qmail + dovecot-1.1.7 + dovecot-sieve + ....
now everything works well but there are many spam in Bulk folders from
every user address to their address for example
from
user1 at mydomain to user1 at mydomain
in the real the sender and reciever are the same .
they are spam but since everyday , everyvirtual user has many of these
spams in their Bulk i need a rule in dovecot.sieve to prevent them
Can anybody help me for writing this rule.
-- 
with regards
Sophia Alikhani
WorkPhone: +98-21-8497057
Mobile : +98-912-3361036