is this illegal? [public email validator overuse]

Not legal advise, but, it sounds like you are simply breaking the terms of service of the email validator website, which is not illegal.

Depends on the country of course but you should be okay.
 
i have similar loophole. i can able to check in real time Phone/Email.
 
Not necessarily illegal. However, collecting or processing email addresses without user consent may constitute a violation of privacy laws.
 
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