[Xylakant]

Do the same thing on the signup page: If the email is already registered just progress the same way - send an email to that address and notify them that they already have an account.

[shinratdr]

Which is great for most accounts, but what about a primary?

How do you sign up for Gmail without an email account in this case?

[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.

[lallysingh]

Use your shudder isp-provided one. Hello [e-mail]

[cryptarch]

ISP email or any provider that doesn't ask for a secondary account, like Mail.com.