It wasn't me, guv'nor!

I opened my email yesterday to find almost 500 messages. I know my site isn’t that popular, so was a bit perplexed until I started reading them – all were returned or undelivered mail referring to messages I had never sent. I contacted the nice web lady in a panic and she told me that my domain had been ‘spoofed’. This means that it looks as though a message comes from my domain but it doesn’t. So please rest assured that I don’t send out sp*m!