[Xylakant]

well, obviously this will not work for a primary account. It also adds friction the signup process, leading to lower conversion rations. But for some use-cases that may be a valid trade-off. Think dating sites, ..., stuff where knowing that a certain email is subscribed already may be embarrassing or worse (gay dating websites in certain countries).

[shinratdr]

Oh absolutely, it's a good system and many sites already utilize it.

I only mentioned the Gmail example because that's what the article was about, it sounded like you were suggesting a solution for that scenario.