Validate an email address in PHP

validEmail.php

<?php
/**
 * Validate an email address.
 * Provide email address (raw input)
 * Returns 1 if the email address has the email
 * address format and the domain exists.
 */
function validEmail($email) {
    $isValid = 1;
    $atIndex = strrpos($email, "@");
    if (is_bool($atIndex) && !$atIndex) {
        $isValid = -1;
    } else {
        $domain = substr($email, $atIndex + 1);
        $local = substr($email, 0, $atIndex);
        $localLen = strlen($local);
        $domainLen = strlen($domain);
        if ($localLen < 1 || $localLen > 64) {
            // local part length exceeded
            $isValid = -2;
        } else {
            if ($domainLen < 1 || $domainLen > 255) {
                // domain part length exceeded
                $isValid = -3;
            } else {
                if ($local[0] == '.' || $local[$localLen - 1] == '.') {
                    // local part starts or ends with '.'
                    $isValid = -4;
                } else {
                    if (preg_match('/\\.\\./', $local)) {
                        // local part has two consecutive dots
                        $isValid = -5;
                    } else {
                        if (!preg_match('/^[A-Za-z0-9\\-\\.]+$/', $domain)) {
                            // character not valid in domain part
                            $isValid = -6;
                        } else {
                            if (preg_match('/\\.\\./', $domain)) {
                                // domain part has two consecutive dots
                                $isValid = -7;
                            } else {
                                if (!preg_match('/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\'*+?^{}|~.-])+$/',
                                                str_replace("\\\\", "", $local))) {
                                    // character not valid in local part unless
                                    // local part is quoted
                                    if (!preg_match('/^"(\\\\"|[^"])+"$/', str_replace("\\\\", "", $local))) {
                                        $isValid = -8;
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
        if (function_exists('checkdnsrr')) {
            if ($isValid && !(checkdnsrr($domain, "MX") || checkdnsrr($domain, "A"))) {
                // domain not found in DNS
                $isValid = -9;
            }
        }
    }

    return $isValid;
}