Have you looked on FeverBee? There are examples of email marketing automation there for Discourse and other platforms.
And there are other useful topics on engagement. Here’s an example using Discourse data queries to drive engagement. It doesn’t specifically involve email marketing automation but it is a useful example and it could feed into an email marketing platform:
https://experts.feverbee.com/t/this-is-the-power-of-discourse/915/12?u=remah