Right now I have a mixed environment of 2003/2007. Going back a few months, my Postmaster account was bombarded with SPAM (thousands), but then I implemented recipient filtering in 2003 with tarpitting rules. The spam went away completely and the only thing in Postmaster was legit msg failures (like 1 or 2 a day).
Fast forward now to 2007 being implemented... Ever since I allowed the new exchange server to start acceping incoming mail from Postini the Postmaster account has been filling up with about 100 SPAM messages a day. I have recipient filtering on with restrictions on incoming IP addresses via SMTP. Obviously there is something missing from my 2007 configuration that it's not working as well as it was in 2003. Any suggestions?