what's wrong with this validation code?

[sridharao]

I have the following code being used for validating a form:

if (isset($_POST['AddEntry'])) {
    $emai = stripslashes($_POST['YourEmail']);
    $namm = stripslashes($_POST['YourName']);
    $commt = ($_POST['YourComment']);
    if (!preg_match("/[A-Za-z]*/", $namm)) {
      die ('<p align="center">Sorry, Please enter text without any symbols or special characters.</p>');  //THIS ISN'T WORKING
    }else{
      $nam = $namm;
   }
    if (!eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$",$emai)){
        die ('<p align="center">There is something wrong with your email ID, please check it.</p>');
    }
    list($userName, $mailDomain) = split("@", $emai);
    if (!myCheckDNSRR($mailDomain, "MX")) {
        die ('<p align="center">Sorry, this email ID failed validation. Please provide correct email ID.</p>');
    }    
    if (!preg_match("/[A-Za-z]*/", $commt)) {
      die ('<p align="center">Sorry, Please enter text without any symbols or special characters.</p>');
    }else{
      $comt = $commt;
   } 

this is the function to check dnserror:

function myCheckDNSRR($hostName, $recType = ''){
    if(!empty($hostName)) {
        if( $recType == '' ) $recType = "MX";
            exec("nslookup -type=$recType $hostName", $result);
            foreach ($result as $line) {
                if(eregi("^$hostName",$line)) {
                    return true;
                }
            }
        return false;
    }
return false;
} 

I found this script on the net for windows based servers, this script is failing despite providing a valid domain name.

[penagate]

I suggest that you don't validate the domain name — it is expensive and prone to failure. It is especially inadvisable in reusable scripts since email addresses need not actually contain a fully-qualified domain name or one which is verifiable using nslookup. For example, mail servers may be able to derive some meaning from particular email addresses even if the domain part of the address is not listed in any local MX record cache or accesible DNS.