it can be done but requires hand coding
2 things you will need to account for:
when a search is preformed, it stores the search parameters in a session variable, this session is used if the results page returnees more results than can be displayed at one time and navigation is used.
you would need to hand code an if statement that checks if the both the email form element and the session are empty. the specifics of the code depend on the method of your search form, the name of the email form element and the name of the session.
if the form uses the GET method, the form element is named "email" and the session that is created is named results, an example would look like this:
<?php
@session_start();
if((!isset($_GET['email']) || $_GET['email'] == "") && (!isset($_SESSION["results"]) || $_SESSION["results"] == "")) {
header("Location: search.php");
}
?>