with the latest update I also activated the Mailing list features of discourse. You can now reply to every topic you receive an email about directly within your email-client by sending a reply-email. Discourse will pick it up and add it to the conversation.
I also activated the Receive-every-email feature. You can now check a box in your preferences that will forward every post made to your email. Excluding - of course - the post and categories you've previously muted. Look for the following:
Those together, discourse now almost acts as (one big) mailing list.