Comment by davemtl

Indeed. I've owned `invaliddomain.com` for almost 20 years. You'll be surprised how many use it for testing. One morning I woke up to 30,000 e-mails from Sony Japan with PDFs attached of scanned hand-written part orders. Something similar with Boeing sending me backup notifications. I notified each of these companies about their configuration through their official channels, only to be told "no, it's your server doing this" then usually followed up with an e-mail a few weeks later along the lines of "sorry, our bad". So, if you're testing something and using a test domain, use the IANA reserved domains, please. Theses were the days when I was running my own servers. I don't see it as often now as my e-mail is now hosted.