A subscription is automatically applied to a user whenever they choose to add a conversation or comment on an existing conversation. This is because when you chose to interact with said document or discussion, the application assumes that it must have some relevance to you, and you will want to be informed on any updates or changes made to them. As a creator of a comment, document or discussion, you will never receive notifications of your own interactions, only those made by fellow users that are subscribed to the same thread.
If you don't wish to remain subscribed, select the 'Unsubscribe' option found above the comment box (top centre of the page) to leave the document/discussion thread. If you wish to become subscribed again at a later date, you can do so using the same method.
Did you know? - You can 'unsubscribe' from a document/discussion thread without having to enter the application. Simply select the link found at the bottom of your email notification relating to the thread to unsubscribe!