Email Address Validate 4 Levels JavaScript PHP Verify

4 different levels of email address validation and verification using JavaScript and PHP. Email address formatting validation can occur on both the client-side and the server-side, but the client-side checks should not be the only validation. Level 1 JavaScript on the client-side of your application

<script>
function isValidEmail(addr){
	var result = false;
	if(addr.indexOf("@") > -1 && addr.indexOf(".") > -1) {
        result = true;
    }
	return result;
}
var address = "namepart@domainpart.com";
alert( isValidEmail(address) );
</script>

<script>
function isValidEmail(addr){
	var regex = /^([w-]+(?:.[w-]+)*)@((?:[w-]+.)*w[w-]{0,66}).([a-z]{2,6}(?:.[a-z]{2})?)$/i;
	var result = false;
	if ( regex.test(addr) ){
		result = true;
	}
	return result;
}
var address = "namepart@domainpart.com";
alert( isValidEmail(address) );
</script>

Level 2 http://php.net/manual/en/filter.examples.validation.php

<?php
$email_a = 'joe@example.com';
$email_b = 'bogus';

if (filter_var($email_a, FILTER_VALIDATE_EMAIL)) {
    echo "This ($email_a) email address is considered valid.";
}
if (filter_var($email_b, FILTER_VALIDATE_EMAIL)) {
    echo "This ($email_b) email address is considered valid.";
}
?>

Level 3 PHP SMTP Email Validation https://code.google.com/p/php-smtp-email-validation/ Level 4 Inbox Click to Verify Email Address https://www.adamkhoury.com/PHP/video/Sign-Up-Form-and-Email-Activation-PHP-MySQL-JavaScript-Programming-Tutorial