From: Arno Hollosi (ahollosixmp.net)
Date: Sun Jan 27 2008 - 09:23:16 CST

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Hello,

I have a problem with backscatter email, which goes like this:

* Setup with two mail servers: TARGET and RELAY (secondary MX)
* RELAY receives email for <valid.usertarget>
   from <forged.senderelsewhere>
* RELAY relays email to TARGET
* TARGET performs a spam check during the SMTP dialog and
   declines email with a "554 5.7.1" status code.
* RELAY produces a bounce message and sends it
   to <forged.senderelsewhere>

RELAY and TARGET are unable to enforce the same spam policies. Thus
RELAY is confronted with 55x responses from TARGET for *valid* users
that in turn produce backscatter bounce messages.

What can I do to stop the backscatter?

Thanks for any hints you can provide.
/Arno

ps: yes, I have read http://www.postfix.org/BACKSCATTER_README.html
But it is only concerned about incoming backscatter, not about outgoing.

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