Not sure if this will help but...i was getting SPAM to my BIS account - however it wasn't actually sent to the address (different address in the To field)
Not sure how it was getting delivered - but it doesn't matter
All i did was set the main filter to "do not forward"to the handheld and set up a filter stating "if any of the following apply...from = my BIS addres then forward to handheld"
i also added my integrated accounts to the same filter
Now i get no SPAM
I also don't get the mailing lists i'm signed up for but i'm not worried since they all contain attachments i don't want to bother opening on my handheld