Reject message no from address

[Paul Lemmons]

This is bound to be an FAQ but for the life of me I can not find the 
answer. After an hour of searching with Google I will accept the flames 
if I missed something obvious.

I would like to reject all messages that do not have a from address with 
a valid syntax. Particularly blank from addresses. We are getting quite 
a bit of "empty spam" (no message, blank sender, blank return path, 
minimal headers) and I would like to filter these messages. Any pointers 
would be helpful.
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