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From: Wietse Venema (wietseporcupine.org)
Date: Mon Nov 16 2009 - 13:54:56 CST
> OK here is the scenario.
> Spammer sends mail to: usermyclientsdomain.com from forged address
> If usermyclientsdomain.com is delivered locally, not a problem, if the
> address is invalid, postix rejects the mail during the smtp connection.
> But if usermyclientsdomain.com is an alias to myclientotherserver.com,
> postfix accepts the mail as deliverable and forwards it to hotmail.com.
> But if myclientotherserver.com can for whatever reason not be
> delivered, otherserver.com does what it is supposed to do and rejects
> the mail during the smtp connection, which causes postfix to send out a
> non-delivery report to victimrandomdomain.com -- backscatter.
> Is there a way to stop this?
Yes. Don't forward SPAM.