Ultimate Email Validation PHP Function

<?php
function validateEmail($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;
  }
?>