You can control whether or not you receive e-mail messages notifying you of activity regarding your account and posts, such as if someone else has shared your post or become a Follower. To see these options, you must be signed in, then go to your user page. From there, click on the button with three bars located to the right of the "Create a new post" button, and select "Notifications". From here you can toggle your options on and off. To see what new notifications you have, click on the Bell icon next to your user name.