Email Validation in PHP

Title says it all but to reemphasize that below PHP code block validate an email address. Its always good to have a client side validation for faster user responses but backend check is also needed for user not having client side scripting on.

PHP:

<?php
    function emailsyntax_is_valid($email) {
      $to_work_out = explode("@", $email);
      if (!isset($to_work_out[0])) return FALSE;
      if (!isset($to_work_out[1])) return FALSE;
    
      $pattern_local = '^([0-9a-z]*([-|_]?[0-9a-z]+)*)(([-|_]?)\.([-|_]?)[0-9a-z]*([-|_]?[0-9a-z]+)+)*([-|_]?);
      $pattern_domain = '^([0-9a-z]+([-]?[0-9a-z]+)*)(([-]?)\.([-]?)[0-9a-z]*([-]?[0-9a-z]+)+)*\.[a-z]{2,4} ;
      $match_local = eregi($pattern_local, $to_work_out[0]);
      $match_domain = eregi($pattern_domain, $to_work_out[1]);
    
      if ($match_local && $match_domain) {
        return TRUE;
      }
      return FALSE;
    }
    ?>

Use the function like this :

PHP:

if (emailsyntax_is_valid($email)) {
      echo "Ok";
    } 
    
    // OR
    
    if (!emailsyntax_is_valid($email)) {
      echo "Invaild";
    }