Validate E-mail Address with PHP the Right Way

Listing 1:  Shows an example code that contains 3 errors. First, it fails to recognize many valid e-mail address characters, such as %. Secondly, it splits the e-mail address into username and domain parts at the sign @. E-mail addresses that contain a quoted @ sign, such as koko@koko@domain.com will break this code. Lastly, it fails to check for host address DNS records.
function validateEmail($email_add) {
    if (preg_match(â€�/^([a-zA-Z0-9])+([a-zA-Z0-9._-])*@([a-zA-Z0-9_-])+( [a-zA-Z0-9._-]+)+$/â€�, $email_add))
      {
          list ($username, $domain)=split(‘@’,$email_add);
          if (!checkdnsrr($domain, ‘MX’)) {
            return false;
          }
          return true;
      }
      return false;
}
Listing 2: Shows a better way to develop an E-mail validator as it satisfy the following requirements:
-An e-mail address consists of local part and domain seperated by an at sign (@) character (RFC 2822 3.4.1)/
-The local part may consist of alphabet and numeric characters, and the following characters: !#$%&’*+-/=?^_`{|}~, possibly with dot seperators (.), inside, but not at the start, end or next to another dot seperator (RFC 2822 3.2.4)
-The local part may consist of a quoted string - i.e. anything within quotes (�), including spaces (RFC 2822 3.2.5)
-Quoted pairs (such as @) are valid components of a local part, though an obsolete form from RFC 822 (RFC 2822 4.4)
-The maximum length of a local part is 64 characters (RFC 2821 4.5.3.1)
-A domain consists of labels seperated by dot seperators (RFC 1035 2.3.1)
-Domain labels start with an alphabet character followed by 0 or more alphabet characters, numeric characters or hyphen (-), ending with an alphabetic or numeric character (RFC 1035 2.3.1)
-The maximum length of a label is 63 characters (RFC 1035 2.3.1)
-The maximum lenght of a domain is 255 characters (RFC 2821 4.5.3.1)
-The domain must be fully qualified and resolvable to a type A or type MX DNS address record (RFC 2821 3.6)
function validateEmail($email_add) {
  $isValid = true;
  $atIndex = strrpos($email_add, “@â€�);
  if (is_bool($atIndex) && !$atIndex) {
        $isValid = false;
  }
  else {
        $domain = substr($email_add, $atIndex+1);
        $local = substr($email_add, 0, $atIndex);
        $localLen = strlen($local);
        $domainLen = strlen($domain);
        if ($localLen 64) {
              $isValid = false; // local part lenght exceeded
        }
        else if ($domainLen 255) {
              $isValid = false; // domain part lenght exceeded
          }
        else if ($local[0] == ‘.’ || $local[$localLen-1] == ‘.’) {
                $isValid = false; // local part starts or ends with ‘.’
        }
        else if (preg_match(’/../’, $local)) {
                $isValid = false; // local part has 2 consecutive dots
        }
        else if (!preg_match(’/^[A-Za-z0-9-.]+$/’, $domain)) {
                $isValid = false; // character not valid in domain part
        }
        else if (preg_match(’/../’, $domain)) {
                $isValid = false; // domain part has 2 consecutive dots
        }
        else if (!preg_match(’/^(.|[A-Za-z0-9!#%&`_=/$’*+?^{}|~.-])+$/’ . str_replace(â€�â€�.â€�”,$local))) {
              if (!preg_match(’/^â€�(â€�|[^â€�])+â€�$/’, $str_replace(â€�â€�,â€�”, $local))) {
                      $isValid = false; //character not valid in local part unless local part is quoted
              }
        }
        if ($isValid && !(checkdnsrr($domain, “MXâ€�) || checkdnsrr($domain, “Aâ€�))) {
            $isValid = false; // domain not found in DNS
        }
    }
    return $isValid;
}