Disallow certain email domains from creating membership(s)

e20r-disabled-domains.php

<?php
/*
Plugin Name: PMPro e-mail domain check
Plugin URI: http://www.paidmembershipspro.com/wp/pmpro-customizations/
Description: Check if a domain is on the "do not allow" list for registration
Version: .1
Author: Stranger Studios
Author URI: http://www.strangerstudios.com
*/

function restrict_email($value)
{
    $email = $_REQUEST['bemail'];

    if(true === is_invalid($email))
    {
        global $pmpro_msg, $pmpro_msgt;

        //TODO: Set the error text to be whatever you want it to be:
        $pmpro_msg = "Please enter a valid email address";
        $pmpro_msgt = "pmpro_error";
        $value = false;
    }

    return $value;
}
add_filter('pmpro_registration_checks','restrict_email', 10, 1);

function is_invalid($email)
{
    $test_domain = getDomainFromEmail($email);
    $invalid_domains = array("yahoo.com", "*.gmail.com", "*.co.uk");

    foreach($invalid_domains as $inv_domain)
    {
        $components = explode(".", $inv_domain);

        if($components[0] == "*")
        {
            unset($components[0]);
            $inv_domain = implode('.', $components);
        }

        if((stripos($inv_domain, $test_domain) !== false))
            return true;

    }

    // The domain specified in the email address is not one of the invalid ones.
    return false;
}

//Taken from: http://www.bitrepository.com/how-to-extract-domain-name-from-an-e-mail-address-string.html
function getDomainFromEmail($email)
{
    // Get the data after the @ sign
    $domain = substr(strrchr($email, "@"), 1);

    return $domain;
}