Often you need to create an account or somehow register your email at sites, just to get something very basic, like a free download, or use a feedback form.

This demonstrates nicely why that's a bad idea.

I entered my address out of curiosity and it told me I had an Adobe account. I can't remember ever creating one so I tried the password reset process. Adobe tells me there doesn't exist an account under that address.

How is this possible? How did Adobe leak my address if I don't even have an account?