You know this is going to be an endless argument because I don't like the RFC either. Blocking NULL sender takes away at least 60% of spam right off the top.
The %age varies by a lot by MX, but I've never seen anywhere near 60%. Maybe your talking about 50% of what get past all your other filtering?
Advanced IMGate allows rules like:
if <no PTR (aka "welcome to my hell")> then reject if: null sender bad helo hostname reject helo if 2-letter TLD
If you can do that in your rules, then you would accept nulsender from legit (business) servers but only outside of the above conditions.
Len
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