When I was a comp sci student in the 90s, I was testing some code where I used foo@bar.com as a placeholder. Amusingly, I got a reply from The Foo, and now I'm glad to know I wasn't the only one who accidentally emailed him/her.
As others have pointed out, username@example.com is a better choice for documentation and examples.
Also see asdf@asdf.com: http://asdf.com/asdfemail.html I've gone to asdf.com for about 15 years now, and it hasn't changed it all. It's also always up, so it's handy to go to to test and see if I have Internet. I love that site.
I wonder if these were the general population of users seen today, since AFAIK foo/bar are not in the vocabulary of most people as metasyntactic variables; I hear "blah" more commonly used for this purpose.
I can't help but think the pricing methodology on this site might be a bit off. I put uw.com in to check it because I know some of the history of that site. It said the site is worth less than $9.00!?
uw.com was originally owned by a company called Underware. Their biggest product was a defect tracking tool called TrackRecord. They were bought by Compuware in the 90s, and in early 2000 or 2001, Compuware forgot to renew the domain and it was bought out from under them. Last I checked, two letter .com domains were pretty rare and valuable.
I also entered addresses I thought were fake. But there are so many registered domain names you can't make sure they are really fake.
[1] https://en.wikipedia.org/wiki/Example.com