When spammers send out hundreds of thousands of emails, they often 'fake' the sender's address by either using a real address found somewhere on the web or just by getting their computer to generate loads of real looking addresses such as
[email protected],
[email protected],
[email protected],
[email protected], etc. Some of those addresses will be entirely imaginary, while others may actually exist
They'll also use the same method for selecting the recipients of the spam messages. (i.e. they might use addresses they know to be real but they're just as likely to make up loads of likely-looking addresses, in the knowledge that some will actually turn out to be real ones).
A spammer has used your email address as the 'return address' in one or more spam messages. There might be loads of people who've received spam which apparently came from you. But at least one of those messages was sent to a non-existent address, so a 'bounce' message has been sent to you (because the receiving server thinks that you sent the spam)..
If you've only received one such message, it's probably just a 'one off' and you can ignore it. However some people are unlucky because a spammer will pick their address as the apparent sender of, say, a million emails. Given that the majority of those mails never get delivered, the innocent person whose address was used might end up with hundreds of thousands of 'bounce' messages flooding into his or her inbox. (For a while, I was getting around 3000 bounce messages per day to one of my email addresses).
Chris