Sounds interesting, but I would need a little explanation of how to set up null sender to trigger SMTP block. Guessing it would block all null senders, which is not what we want as there are a lot of legit messages.
Hoping to just have a checkbox so it can assign 10-15 points and when it combines with another RBL, SPF, etc. it will get blocked. That will allow the legit bounces in and reject the spam.