> ... how to notify the node author when new comments are posted on their content??

I'm [a bit](https://drupal.stackexchange.com/search?tab=votes&q=user%3a39516%20%5brules%5d) familiar with the (amazing!) [Rules](https://www.drupal.org/project/rules) module. But to my knowledge the current answer to this question is ***Not possible yet***.

### More info

- Refer to [#d8rules status update November 2017](http://d8rules.org/news/d8rules-status-update) to get a better understanding of the current status of Rules for D8. Here are some (scary) quotes from it:

  > - ... Fago can’t dedicate time required to develop the module further. What Rules is really missing at the moment is development capacity to help finish the last milestone.

  > - ... Even if we got more funding today, fago the current principal maintainer of the Rules module wouldn’t have enough capacity to do the work himself.

- Start [here](https://drupal.meta.stackexchange.com/a/3616/39516) if you wonder how to contribute.

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<sup>One never realizes what ***has been*** done, only what ***remains to be*** done ...</sup>

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### Plan B

You might want to look at the [Message](https://www.drupal.org/project/message) module (and the related modules that belong to the Message Stack), which has a pretty stable release already, and which you could use to create similar functionality.