Backscatter

It may happen that you suddenly receive a lot of “undeliverable” notices for emails that you never sent.

What you’re seeing are bounce messages from forged headers sent in spam or viruses, called “backscatter”.

Note that it does *not* mean someone has “hijacked” your email; merely that someone is lying about the reply-to address for emails they’re sending out.

Backscatter is most commonly seen as an effect of a particular type of virus that effects Microsoft Outlook and Outlook Express. The way it works is this: A computer becomes infected when the user opens an email that contains this virus. This computer will then mail out copies of the virus to a list of email addresses generated from the address book of the infected computer. It then selects another email address from the inbox of that same computer and uses it as the return address. So the email appears to be coming from someone else. Many email systems are now protected against this virus, so some of the emails that the infected computer is sending out are rejected by the recipients server, and bounces back to the sender, which in this case appears to be you!

So by getting these messages, it does not mean that your computer is infected, just that you have probably sent email to someone else who’s computer WAS infected.

Unfortunately, there isn’t anything you can do to prevent the emails from coming to you, short of changing your email address. We recommend just setting up a filter (aka Mail Rule) in your email client software to automatically delete any messages coming from “Mailer-Daemon” or “Mail Delivery Subsystem”

Please see also http://spamlinks.net/prevent-secure-backscatter.htm