PHP 验证Email的函数

<?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)      {         // 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;} ?>