These people spoof your email.
We’ve had some extreme cases in the past, with a big time spammer taking revenge by spoofing zillions of mails from one of our member addresses.
This one didn’t hit me big time, but one such person hacked their way into my server and used one of my domains and my server to send phishing mails.
I ended up having to abandon the domain and the server, and luckily was able to prove that I was hacked – otherwise I would have gone to jail to boot!
Internet advertising has a criminal element. We see it in spam, phishing, dozens of scams to cheat people out of their money and more often than not it is done from hijacked or spoofed addresses.