Checking the validity of your Google account

I’ve come across sites online that quickly check a large number of Google accounts for validity. Without logging into your account, only by login.
How it works? Share your knowledge please

maybe they linked to the database by some means and then made a comparison. that's just my humble opinion.

accs_pax said:

I’ve come across sites online that quickly check a large number of Google accounts for validity. Without logging into your account, only by login.
How it works? Share your knowledge please

Click to expand...

If you enter your login while logging in and it asks for a password or for a captcha, the account exists. If it shows a red text, the account doesn't exist. This is the only way of making sure whether an account exists. You only enter your login, you don't access the account.
All other methods, like the last person said, compare your accounts list with their accounts list, which is supposed to contain mostly existing accounts; so the question here would be how they have obtained that list. These services usually explain how they made the list for comparison. This method would approximately show which accounts are valid and which aren't, but of course it would also skip some valid and/or count some invalid accounts as valid.

Account verification is carried out without a proxy. They check up to 10 thousand logins at a time, within 5 minutes.
I think that there are requests to the mail server, for example MX, and it gives some kind of response that contains information whether this account is valid or not.

Does anyone know anything about this?