Force users to be logged-in to download purchased files through Easy Digital Downloads and also require the account email match the purchase email
<?php
/*
 * Plugin Name: Easy Digital Downloads - Restrict Downloads to Purchase Email
 * Description:
 * Author: Pippin Williamson
 * Author URI: https://easydigitaldownloads.com/
 * Version: 1.0
 */

class EDD_Force_Login_And_Email {

	function __construct() {
		add_action( 'plugins_loaded', array( $this, 'load' ) );
	}

	public function load() {
		add_filter( 'edd_file_download_has_access', array( $this, 'check_access' ), 9999, 3 );
	}

	public function check_access( $has_access, $payment, $args ) {

		if( ! is_user_logged_in() ) {
			$has_access = false;
		}

		$customer = new EDD_Customer( edd_get_payment_customer_id( $payment ) );

		if( ! in_array( $args['email'], $customer->emails ) ) {
			$has_access = false;
		}

		return $has_access;

	}

}
$GLOBALS['edd_force_login_and_email'] = new EDD_Force_Login_And_Email();
To implement this snippet on your site, create a brand new, empty WordPress plugin and paste the above code inside.