How do I use message stack (or other) to send new blog post (nodes) to "email-only subscribers" like Wordpress?
There are three modules that support this type of subscription and notification workflow without requiring subscribers to actually be registered users on the Drupal site:


Simple Subscription https://www.drupal.org/project/simple_subscription
Total Subscription https://www.drupal.org/project/total_subscription
Simple News https://www.drupal.org/project/simplenews


Below are some notes and caveats to each module/approach:


Simple Subscription: the 7.x-1.x branch provides the basics, but hasn't seen much maintenance/activity since the move toward the 7.x-2.x alpha in 2016.  The alpha has some nice features and intent, but is also just an alpha release.  This module has token support and can work nicely with out of the box rules based messaging.
Total Subscription: This module does not offer to site managers any administrative functionality to unsubscribe email addresses or toggle on/off notifications for testing purposes. You'd have to enable/disable the module to toggle notifications (all or nothing) for any content types or taxonomies setup to publish subscription notifications.  Custom html email templates can be generated with the HTML Mail module, but templating only supports the default body/summary field and not any custom fields applied to the content type.  Messages are queued and sent via Drupalcron.
SimpleNews: This module is probably the most stable of the options and offers a D8 version; but it requires the extra step for content managers having to switch to the Newsletter tab and manually send the notifications after node creation.