If you encounter it – and a rapidly increasing number of people do – you certainly know about it; while most spam emails just regularly drop into your inbox every few minutes (or hours, if you're lucky) backscatter tends to flood you with an enormous number of spam messages in a very short space of time. You can recognise them because they all look like emails that have bounced back; mainly "User not known" messages, but also a load of "Out of office reply" messages, too, and all in response to a spam email that appears to have been sent from your address. People's immediate response is to think "Oh no, I've got a virus"; while that's not impossible, it's far more likely that a spammer has just chosen your email address as the one to put into the "From:" line of the spam message. So it looks as if it came from you, where in fact it's merely the equivalent of someone else signing your name at the bottom of a letter.

Backscatter is incredibly annoying; aside from the sheer number of messages you have to deal with, you also have to cope with the inevitable furious responses from people who did get the spam message and think that you sent it to them; there's also the possibility that your email address could be blacklisted. And backscatter is in itself spam; it often containing the contents of the bounced spam message and, worse, it originates from perfectly valid mail servers that are simply set up to reject emails sent to non-existent accounts. One way of cutting backscatter would be for hosting provider to set up their mail servers not to bounce messages to unknown users; AOL have done so and virtually eliminated their role in the problem. But then again, if you do send an email to an elapsed AOL account, you won't be notified. But maybe that's a small price to pay to slash the amount of spam circulating.

Systems such as SPF are designed to prevent backscatter by allowing you to tell your email or hosting provider which machines are allowed to send email that purports to come from you – but it's not particularly user friendly (yet) and often requires you to get under the bonnet of your hosting settings. But there's one thing you can do immediately if you have your own domain – such as independent.co.uk – and that's to make sure that you're not receiving emails for any address on your domain – for example xyzxyz@independent.co.uk – and only for addresses that you actually use. It should be easy to turn this off with your hosting provider. In fact, it's incredible that any provider still chooses to enable it by default.

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