Email validation using regular expression in PHP

Question

I am pretty much new with regular expression. I am developing a project in PHP and i need to validate email address. After searching in this site and google i found the fol

Answer 1

There more than one ways to check if an e-mail is valid.

One simple way is to use this function:

function validate($email) {
    return preg_match("/^[a-zA-Z0-9_.-]+@[a-zA-Z0-9-]+.[a-zA-Z0-9-.]+$/", $email);    
}

It is from a code snippet found here: Basic Email Validation in PHP

Although this implementation would work most of the time it may allow some wrong emails. The following implementation ahould be 100% accurate but is also quite complex:

function validate($email) {

    $isValid = true;
    $atIndex = strrpos($email, "@");

    if (is_bool($atIndex) && !$atIndex) {
        $isValid = false;
    } else {
        $domain = substr($email, $atIndex + 1);
        $local = substr($email, 0, $atIndex);
        $localLen = strlen($local);
        $domainLen = strlen($domain);

        if ($localLen < 1 || $localLen > 64) {
            $isValid = false;
        } else if ($domainLen < 1 || $domainLen > 255) {
            $isValid = false;
        } else if ($local[0] == '.' || $local[$localLen - 1] == '.') {
            $isValid = false;
        } else if (preg_match('/\\.\\./', $local)) {
            $isValid = false;
        } else if (!preg_match('/^[A-Za-z0-9\\-\\.]+$/', $domain)) {
            $isValid = false;
        } else if (preg_match('/\\.\\./', $domain)) {
            $isValid = false;
        } else if (!preg_match('/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\'*+?^{}|~.-])+$/', str_replace("\\\\", "", $local))) {
            if (!preg_match('/^"(\\\\"|[^"])+"$/', str_replace("\\\\", "", $local))) {
                $isValid = false;
            }
        }

        if ($isValid && !(checkdnsrr($domain, "MX") || checkdnsrr($domain ,"A"))) {
            $isValid = false;
        }
    }

    return $isValid;
}

This code is from snippet found here: Strict Email Validation in PHP

Hope this helps!