php 邮箱验证函数

function checkEmail($email) 
{
   // Create the syntactical validation regular expression
   $regexp = "^([_a-z0-9-]+)(\.[_a-z0-9-]+)*@([a-z0-9-]+)(\.[a-z0-9-]+)*(\.[a-z]{2,4})$";
 
   // Presume that the email is invalid
   $valid = 0;
 
   // Validate the syntax 字符串比对解析，与大小写无关。
   if (eregi($regexp, $email))
   {
      list($username,$domaintld) = split("@",$email);
      // Validate the domain
      if (getmxrr($domaintld,$mxrecords))
         $valid = 1;
   } else {
      $valid = 0;
   }
 
   return $valid;
 
}