We're using a Linux mailfilter/smarthost to filter email and tag it as spam before it reaches the Exchange 2010. Email that is over a certain threshold is simply dropped, but some small amount of spam gets tagged [SPAM] and delivered. Unfortunately when one of those messages hits a user's mailbox that has an out of office auto-response, our Exchange server obligingly tries to send an automatic response. Since obviously these messages are being sent to bogus domains/email addresses, they just rot in the queue until they time out completely.
Is there any way to drop these auto responses instead of sending them?