I got email notifications correctly on the same comment on the same issue on Taiga (about Spamhaus).
Hm, created the Discourse account a few days ago, never had one before, didn’t change any settings, never got a notification by email:
Then just now, after you replied, I went to settings again and pressed the Save Changes button without changing anything, notice the Activity Summary section changed a bit:
Try to reply to this one, as a test. Maybe saving changes did something.
Just to update that reply notifications are working correctly, both in the web UI and by email.