Just found this very simple & efficient way of validating email address with PHP.
You can use this to replace the usual regular expression email checking.

<?php
$email = "john@doe.com";

if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
      echo "Please check your email address";
} else {
      echo "Great! valid email address";
}
?>

Source:

http://www.php.net/filter_var