I used to do this (now I use less guessable keys) and recall having many similar conversations. Occasionally I would run into someone who refused to believe the

I used to do this (now I use less guessable keys) and recall having many similar conversations. Occasionally I would run into someone who refused to believe the address was "real" but then when I gave them some other arbitrary string at the same domain they suddenly accepted it. I've also encountered websites which refused to let me sign up with their company's name anywhere in the email string and one particularly hilarious example where the site accidentally gave me access to things I wasn't supposed to have access to just because I'd used site.com@mydomain.com to sign up.