The DomainWhitelist plugin restricts the email addresses in a domain to a
select whitelist.

Installation
============
add "addPlugin('DomainWhitelist');"
to the bottom of your config.php

Settings
========
whitelist: An array of whitelisted domains

Example
=======
$config['email']['whitelist'] = array('example.org', 'example.net');
addPlugin('DomainWhitelist');