Verify users email

Question

When a user sets up an account for an application and uses their email address for a username, how do I verify that the email address they entered is a valid email? Specifically, without sending a verification email.

Answer 1

1. Valid e-mail address eq php filter_var('root@stackoverflow.com', FILTER_VALIDATE_EMAIL);
2. when user finish retyping e-mail onfocus send ajax request
3. DNS query for e-mail svr eq search in google for source script "valid email by dns github"