Validate an EMail Address in PHP, the Right Way

/**
SOURCE: http://www.linuxjournal.com/article/9585

Validate an email address.
Provide email address (raw input)
Returns true if the email address has the email
address format and the domain exists.
*/

function validEmail($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) {
      // local part length exceeded
      $isValid = false;
    } else if ($domainLen < 1 || $domainLen > 255) {
      // domain part length exceeded
      $isValid = false;
    } else if ($local[0] == '.' || $local[$localLen-1] == '.') {
      // local part starts or ends with '.'
      $isValid = false;
    } else if (preg_match('/\\.\\./', $local)) {
      // local part has two consecutive dots
      $isValid = false;
    } else if (!preg_match('/^[A-Za-z0-9\\-\\.]+$/', $domain)) {
      // character not valid in domain part
      $isValid = false;
    } else if (preg_match('/\\.\\./', $domain)) {
      //domain part has two consecutive dots
      $isValid = false;
    } else if (!preg_match('/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\'*+?^{}|~.-])+$/', str_replace("\\\\","",$local))) {
      // character not valid in local part unless
      // local part is quoted
      if (!preg_match('/^"(\\\\"|[^"])+"$/', str_replace("\\\\","", $local))) {
        $isValid = false;
      }
    }
    if ($isValid && !(checkdnsrr($domain,"MX") || checkdnsrr($domain,"A"))) {
      // domain not found in DNS
      $isValid = false;
    }
  }
  return $isValid;
}

<?php
$valid = preg_match('#<([a-z0-9.!\#$%&\'*+-/=?^_`{|}~]+@([0-9.]+|([^\s]+\.+[a-z]{2,6})))>#i', $email, $matches);
?>

<?php
$valid = preg_match('#<([a-z0-9.!\#$%&\'*+-/=?^_`{|}~]{1,64}@([0-9.]+|([^\s]+\.+[a-z]{2,6})))>#i', $email, $matches);
?>