If you haven't changed a lot of settings in your Facebook account, chances are you get all those email notifications from Facebook by default. The company is refreshing the email system. Instead of sending out each and every notification to you by email, Facebook will not automatically send you a summary email with stuff that matters to you.
Facebook is announcing these news by email. Even if you have opted out of every email notification, you will receive an email that will explain this to you. At the same time, the new 'summary email' feature will get turned on by default.
Of course, the individual email notifications will also be available for users to turn back on.