Auto case creation on email prob: Spam

We're in the final phases of testing before NS launch. Our NS team configured automatic case creation upon email receipt, which also auto notifies the sender from an email template. We're using an address from our own domain that is forwarded (through AD/Exchange) to the NS address.

The problem is, a lot of spam gets in causing unwanted case & e-mail reply generation. The real problem is that our anti-spam solution is tag & pass, so even caught spam is still passed on (false-positive paranoia on the part of the business). For Outlook users this isn't a problem, because it is automatically sent to Junk E-mail, but I'm trying to find a way to filter it for NS.