> I was thinking of rejecting mail when the MAIL FROM is empty or set to > <> during the MAIL FROM stage.
Do not. "<>" is the legitimate envelope sender for bounce messages and
shall never be blocked. Unfortunately this can be abused by spammers,
but it is nevertheless harmfull to block "<>".
Regards
Michael
--
It's an insane world, but i'm proud to be a part of it. -- Bill Hicks
