<?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;
}
?>