[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
us...@mydomain to us...@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