Magento Module issue

I took the code from a StackOverflow post to build a module to accept only certain coupons for customers with a certain email domain for Magento v 1.0.4.1 (Yes, I know it is old but we cannot upgrade due to core modifications by a contractor so do not ask)
 
This is the code (located in /app/code/local/NA/LimitCoupon/Module):

 
<?php
class NA_LimitCoupon_Model_Observer 
{
    protected $_domainsAllowed = array(array('COUPON1', 'email1.com'), 
                                        array('COUPON2', 'email2.com')
                                      );

    public function validate(Varien_Event_Observer $observer)
    {

$timestamp = date("m-d-Y H:i:s");
$msg = "Timestamp:".$timestamp;
$fp = fopen("/var/tmp/".__FUNCTION__.".txt", 'a');
fwrite($fp, $msg . "\n");
fclose($fp);

        try 
        {
            $this->validateRestriction($observer);
        }
        catch (Mage_Core_Exception $e) 
        {
            Mage::getSingleton('checkout/session')->addError($e->getMessage());
        }
        catch (Exception $e) 
        {
            Mage::getSingleton('checkout/session')->addError($this->__('Cannot apply the coupon code.'));
            Mage::logException($e);
        }
    }


    public function validateRestriction(Varien_Event_Observer $observer)
    {



        $errMsg = false;
        // Get the quote: 
        $quote = $event->getQuote();
        // obtain the code being used
        $code = $quote()->getCouponCode();
        // Get the current quote email
        $currentEmail = $quote()->getCustomer()->getEmail();
        $explodedEmail = explode('@', $currentEmail);

        // Get the domain from the email address
        $domain = array_pop($explodedEmail);

$timestamp = date("m-d-Y H:i:s");
$msg = "Timestamp:".$timestamp."\nCode: ".$code."\nCurrentEmail: ".$currentEmail."\nDomain: ".$domain;
$fp = fopen("/var/tmp/".__FUNCTION__.".txt", 'a');
fwrite($fp, $msg . "\n");
fclose($fp);

        switch($code) 
        {
            case 'COUPON1':
                // check if the email address is in the email1 domain        
                if ($domain !== $this->_domainsAllowed[$code]) 
                {
                   // Wrong domain
                   $errMsg = 'This coupon code is restricted to customers of EMAIL1';
                }
                break;
            case 'COUPON2':
                // check if the email address is in the email2 domain        
                if ($domain !== $this->_domainsAllowed[$code]) 
                {
                   // Wrong domain
                   $errMsg = 'This coupon code is restricted to customers of EMAIL2';
                }
                break;
        }
        // handle errors
        if ($errMsg) 
        {
            Mage::getSingleton('checkout/session')->addError($errMsg);
            $quote->setCouponCode('');
            $quote->collectTotals()->save();
        }
    }
 

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And the module XML file (located in /app/etc/modules):

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

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And the config.xml (located in /app/code/local/NA/LimitCoupon/etc):

 <?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <NA_LimitCoupon>
            <version>0.0.1</version>
        </NA_LimitCoupon>
    </modules>
    <global>
        <models>
            <module>
                <class>NA_LimitCoupon_Model</class>
            </module>
        </models>
        <events>
            <salesrule_validator_process>
                <observers>
                    <LimitCoupon_validate>
                        <type>singleton</type>
                        <class>module/observer</class>
                        <method>validate</method>
                    </LimitCoupon_validate>
                </observers>
            </salesrule_validator_process>
        </events>
    </global>
</config>
 

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The issue is, it never goes into the code at all, hence the lack of anything written to the /var/tmp directory as it should be from my FWRITE commands. What am I doing wrong here?
 
Essentially, I want to limit usage of COUPON1 to customers with email1.com in their email address and usage of COUPON2 to customers with email2.com in their email address.