Introduction

Backscatter (also known as outscatter, misdirected bounces, blowback or collateral spam) is a side-effect of e-mail spam, viruses and worms, where email servers receiving spam and other mail send bounce messages to an innocent party. This occurs because the original message's envelope sender is forged to contain the e-mail address of the victim. A very large proportion of such e-mail is sent with a forged From: header, matching the envelope sender.

In this example, we filter backscatter messages into a folder called Backscatter. To automatically delete them, replace target location Backscatter with /dev/null.

Rules

:0:
*^From: .*MAILER-DAEMON.*$
*X-Spam-Status: .*ANY_BOUNCE_MESSAGE.*$
Backscatter

:0:
*^From: .*Mail Delivery System.*$
*X-Spam-Status: .*ANY_BOUNCE_MESSAGE.*$
Backscatter

:0:
*^Subject: .*Undeliverable.*$
*X-Spam-Status: .*ANY_BOUNCE_MESSAGE.*$
Backscatter

References

1. http://en.wikipedia.org/wiki/Outscatter
2. http://www.spamresource.com/2007/07/ask-al-my-email-address-is-being-use...