Backscatter is spam that uses a fake sender field, causing undeliverable mail notifications to be sent to innocent people. Spammers obtain valid email addresses through various means and the best defense is to use a smart spam blocker with Bayesian filtering. It’s not recommended to reply to spam or unsubscribe. If you own a domain, configure your mail servers to not use the catch-all option. Reporting spam can be done through services like the Federal Trade Commission or Spamcop.
Backscatter, as far as email is concerned, is spam that contains a spoofed Sender field, causing rejected mail to be “returned” to an innocent person who was not the real source of the spam. Those “undeliverable mail” notifications in your inbox that weren’t sent by you in the first place are backscatters from spammers illegally using your email address.
Spammers know that most mail servers won’t route mail without a valid sender field. Once spam became illegal, spammers stopped using their own addresses and started forging other valid addresses. Spammers can obtain valid email addresses using any number of means, including software bots that scan the web for email addresses on web pages. Spamming software can also generate addresses by assigning common names to Internet service providers Established (ISP) and mailing lists are another source.
Once your email address appears on a spammer’s list, spam will be generated with your address as the sender. Spam that doesn’t make it to a valid recipient or is rejected for another reason is returned as undeliverable, as backscatter.
The rule of thumb for receiving spam is to not reply, even to say, “Please unsubscribe me from your list!” It won’t do any good anyway, since the “sender” is spoofed. You’ll only end up sending mail to people who are victims themselves, making the problem worse.
If you like, you can report spam to your preferred service, such as the Federal Trade Commission (US), Spamcop or others. These services try to trace the true origin of the spam. If you choose to report spam, read the site’s instructions first, as some information is required to track email, including email headers.
The end user’s best defense in dealing with backscatter is to use a good smart spam blocker that will clean the backscatter out of your inbox before you even see it. The best programs use Bayesian filtering to actively “learn” which mail you do and don’t want. By initially training the filter, it will soon start filtering without requiring your input, dramatically reducing the amount of spam that reaches your inbox. After a period of a few months, a good spam filter should require very little input.
If your email program doesn’t have a built-in Bayesian filter, try a free Bayesian filter like PopFile, SpamBayes, or K9. These and other third-party programs will work with any email client.
If you own one or more domains, configure your mail servers to not use the catch-all option. This will cause the server to reject all mail that is not addressed to a real address on the domain. With the “catch-all” option enabled, all mail sent to (anyone)@yourdomain.com will pass as a “valid” email address, potentially generating ever-increasing volumes of backscatter.
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