Restrict mail TLD registration.php

<?php
/**
* Plugin Name: Restrict mail TLD registration
* Plugin URI:  http://samelh.com
* Description: Allow/disallow user registration for email TLD
* Author:      Samuel Elh
* Author URI:  http://samelh.com
* Version:     0.1
*/

function se__verify_tld( $email ) {

	/* enter the TLDs to allow into following array, e.g array( "be", "nl", "cr" ) in lowercase */
	$allowed_tlds = array( "be", "nl" ); // allowing Belgium and Netherlands emails

	/* OR, enter few TLDs to prevent (forbidden) in lowercase */
	$forbidden_tlds = array();

	if ( empty( $email ) ) return false;
	$tld = strtolower( substr( $email, strpos( $email, '.' )+1 ) );
	if ( empty( $tld ) ) return true; // no tld caught, trigger error
	else $tld = strtolower( $tld );
	
	if ( !empty( $forbidden_tlds ) ) {
		if ( in_array($tld, $forbidden_tlds) ) {
			return true;
		}
	}

	else if ( !in_array($tld, $allowed_tlds) ) {
		return true;
	}

	return false;

}

add_filter( 'registration_errors', function( $errors, $user_login, $user_email ) {

	if ( se__verify_tld( $user_email ) ) {
		$errors->add( "tld_exception", "Sorry, you can not sign up with emails from this TLD" );
	}

    return $errors;

}, 10, 3 );