Yes. At the bottom of each email is an unsubscribe link:
"You are receiving this email because <your email address> is enrolled in <course name> To stop receiving similar future emails from this class, please click here. Please do not reply directly to this email. If you have any questions or feedback, please post on the class discussion forums. For general questions, please visit our support site."
Clicking this link will unsubscribe you from all communications from this course, including important communications from course staff. If you wish to unsubscribe only from a particular forum thread, go to the given forum thread (there will be a link to it from the email verification you received) and unsubscribe by clicking the Unsubscribe button in top-right corner of that thread.
If you do not wish to receive updates from threads you post on, please make sure to un-click the Subscribe button at the bottom of that thread when you go to post!