MailPoet comes with a “subscribe in comments” option that allows visitors who comment on a post to subscribe to your list via a checkbox. But this box is unchecked by default. With this jQuery snippet, you can have the box auto-checked on page load.
You may need to do redirections on your WordPress site from time to time. While they can be done with PHP or via code tweaks in your .htaccess file, this article explains a simpler and more robust method involving the WordPress Redirection plugin.