Hi,
All email hits your Inbox first then within seconds it gets filtered and sent to SPAM or other folders based on your rules.
What's happening is that your Redirector is occasionally catching the SPAM email before it was taken out of the inbox by Outlook.
(free option) To fix this you might be able to create a rule in Outlook to forward all your Inbox email to a new folder called "spam-free" and run this rule after all the other rules have run. Then setup redirector to only forward the "spam-free" folder to your BlackBerry.
(paid option) If this does not work, then you could pay for a software or service like
www.inboxer.com or
www.spamarrest.com to filter your spam.
Hope that helps.
By the way, check out our great BlackBerry Videos & eBooks at our web site. (in my signature).
Thanks,
Martin