mklasen

<?php
/**
 * Plugin name: Allow email as WordPress Network/Multisite username
 * Description: A wordpress mu-plugin that allows you to create users with email-addresses as usernames in multisite
 * Version: 1.0
 * Author: @anttiviljami
 * License: GPLv3
 */

add_filter( 'wpmu_validate_user_signup', '_signup_allow_email_as_username' );