Magento Commerce, 2.2.x
Order Status Notification

Customers can track the status of their orders by RSS feed if the Order RSS feedReally Simple Syndication: A technology that creates web content syndication and allows web users to subscribe to product feeds, websites, and blogs. is enabled in the configuration.  When enabled, a link to the RSS feed appears on each order.

To enable Order Status Notification:

1. On the Admin sidebar, tap Stores. Then under Settings, choose Configuration.
2. In the panel on the left, under Catalog, choose RSS Feeds.
3. Expand the Order section.
4. Set Customer Order Status Notification to “Enable”.
5. When complete, tap Save Config.