Commenting on an existing discussion post, you will automatically be set to follow the discussion post to receive email updates regarding the subject topic.
You will receive email notifications with direct links to the post, as shown below.
If at any point you would like to unfollow from the email updates, you can do so from the email directly or from the "Stop Following" link on the discussion.
To view all discussion posts that you are currently following, you may choose the "Posts I'm Following" filter. First looking for the icon as shown below.
For more information on navigating through discussions, visit this article.