[dredmorbius]

It appears you're missing the main point of the parent post.

You cannot validate an email address.

You can make a basic excruciatingly simple test for proper form. And should probably limit your checks to that.

For all else, attempt to use the email address provided for validation within your onboarding loop with a sufficiently unique verification URL or code. If that succeeds, the address is ... still not absolutely certainly valid, as it may have gone to a third party who proceeded to verify it. But at least it delivered to somebody.

See: https://hackernoon.com/the-100-correct-way-to-validate-email...