PHP contact form - making a field not mandatory -

how can make "email" field not mandatory? if not filling field, form should submit.

in below code, "email" field mandatory.

i tried add if !isset email field $email_from word "empty", didn't work me.

<?php if(isset($_post['name'])) {        // edit 2 lines below required      $email_to = "aaaaa@aaaaa.com";      $email_subject = "messeage site";         function died($error) {      ?>    <?php          die();      }         // validation expected data exists      if(!isset($_post['name']) ||          //!isset($_post['email']) || /* tried comment line, didnt work. */          !isset($_post['telephone'])) {          died('we sorry, there appears problem form submitted.');             }       $name = $_post['name']; // required      $email_from = $_post['email']; // required      $telephone = $_post['telephone']; // not required       $error_message = "";      $email_exp = '/^[a-za-z0-9._%-]+@[a-za-z0-9.-]+\.[a-za-z]{2,4}$/';    if(!preg_match($email_exp,$email_from)) {      $error_message .= 'the email address entered not appear valid.<br />';    }        if(strlen($error_message) > 0) {      died($error_message);    }      $email_message = "form details below.\n\n";        function clean_string($string) {        $bad = array("content-type","bcc:","to:","cc:","href");        return str_replace($bad,"",$string);      }        $email_message .= "first name: ".clean_string($name)."\n";      $email_message .= "email: ".clean_string($email_from)."\n";      $email_message .= "telephone: ".clean_string($telephone)."\n";       // create email headers  $headers = 'מאת: '.$email_from."\r\n".  'חזור ל: '.$email_from."\r\n" .  'x-mailer: php/' . phpversion();  @mail($email_to, $email_subject, $email_message, $headers);    ?>  <?php     echo '<meta http-equiv="refresh" content="0; url=thank_you.html">';         exit;        ?>    <?php    }  ?> 

 if(!isset($_post['name']) ||  !isset($_post['telephone'])){   if(isset($_post['email'])){ //all code email inside here } } 

this should trick, while $_post['email'] empty should´t bother anymore.