BB Torch :: Filters Don't Seem To Work - 9800 Stops Receiving All Emails

I've been getting an incredible amount of spam recently. So I've tried setting up filters on my BB Torch 9800. If I set up only two or three filters, it seems to work fine. But if I set up more than that, the BB just stops receiving all emails, not just the filtered ones. I've checked to see that I've clicked the right options. I'm not, apparently. So what's the trick to setting up lots of filters to kill of this wretched spam? In Outlook, of course, it's easy -- I can set up rules to stop the **bleep** reaching my in-box -- and I was hoping it was going to be similarly easy to do on the BB. But it isn'.