PHP 验证Email的函数

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] == &#39;.&#39; || $local[$localLen-1] == &#39;.&#39;)
      {
         // local part starts or ends with &#39;.&#39;
         $isValid = false;
      }
      else if (preg_match(&#39;/\\.\\./&#39;, $local))
      {
         // local part has two consecutive dots
         $isValid = false;
      }
      else if (!preg_match(&#39;/^[A-Za-z0-9\\-\\.]+$/&#39;, $domain))
      {
         // character not valid in domain part
         $isValid = false;
      }
      else if (preg_match(&#39;/\\.\\./&#39;, $domain))
      {
         // domain part has two consecutive dots
         $isValid = false;
      }
      else if
(!preg_match(&#39;/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\&#39;*+?^{}|~.-])+$/&#39;,
                 str_replace("\\\\","",$local)))
      {
         // character not valid in local part unless 
         // local part is quoted
         if (!preg_match(&#39;/^"(\\\\"|[^"])+"$/&#39;,
             str_replace("\\\\","",$local)))
         {
            $isValid = false;
         }
      }
      if ($isValid && !(checkdnsrr($domain,"MX") || checkdnsrr($domain,"A")))
      {
         // domain not found in DNS
         $isValid = false;
      }
   }
   return $isValid;
}
 
?>