Emails, a way for other people to put things in your todo list. Just reading the email is a task that you might not have planned. Then it's website to check, videos to see, answers to writes.
Planning when you check your inbox is a good start. Two to three times a day is probably enough. Then take the habit to unsubscribe to every email you didn't find very important. The "mark as spam" button is also useful for messages that are not 100% spam, but are still annoying.