Magento customer group registration specific domain

config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Rifki_MembershipGroup>
            <version>0.0.1</version>
        </Rifki_MembershipGroup>
    </modules>
    <global>
        <models>
            <rifkimembershipgroup>
                <class>Rifki_MembershipGroup_Model</class>
            </rifkimembershipgroup>
        </models>
        <events>
            <customer_save_before>
                <observers>
                    <rifki_membershipgroup_observer>
                        <type>singleton</type>
                        <class>Rifki_MembershipGroup_Model_Observer</class>
                        <method>changeCustomerGroup</method>
                    </rifki_membershipgroup_observer>
                </observers>
            </customer_save_before>
        </events>
    </global>
</config>

Observer.php

<?php
/**
 * Observer change Customer group
 *
 * @category    	Rifki
 * @package     	Rifki_MembershipGroup
 * @author		    Muhamad Rifki
 * @copyright   	rifkilabs.net
 */
class Rifki_MembershipGroup_Model_Observer
{
    const STUDENT_CUSTOMER_GROUP = 7; // your customer group_id
    private static $domainRegisters = [
        ’yourschool1.sch.id',
        'yourschool2.sch.id',
    ];

    // filter by domain name for change Customer group
    public function changeCustomerGroup(Varien_Event_Observer $observer)
    {
        $customer = $observer->getEvent()->getCustomer();
        list($user, $domain) = explode('@', $customer->getEmail());

        if (in_array($domain, self::$domainRegisters)) {
            Mage::log('email => '.$customer->getEmail(), null, 'membership_student.log');
            $customer->setData('group_id', self:: STUDENT_CUSTOMER_GROUP);
        }
    }
}

Rifki_MembershipGroup.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <Rifki_MembershipGroup>
            <active>true</active>
            <codePool>local</codePool>
        </Rifki_MembershipGroup>
    </modules>
</config>