fetchmail and spam assassin

[dave]

Hello,
Does anyone have fetchmail retrieving mail from an ISP account then sending
it through spamassassin/an MTA junk mail filter? I've got an account that is
being spammed and i'd like to set this up, but although i can retrieve the
mail via fetchmail, i can not get it to go through postfix which is running
on the same box and which has spamassassin and some other anti-uce filters
in place.
 Also on the subject of spamassassin a lot of junk is still getting through,
is there a FreeBSD specific spam assassin configuration tutorial or howto?
Thanks.
Dave.