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(EditHint: Are you saying don't bounce at all ? Or is there an envelope-from that's different from the "From:" in the subject line that I *can* bounce to ?) Reply: don't bounce spams at all. You can't trust any portion of the message, including the envelope info. If you bounce spam, you're just contributing to the effectiveness of Joe Jobs.
Here's a recipe that I use with qmail and maildrop (if you use e.g. sendmail and procmail instead, it will not work) to delete and bounce all spam messages:
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