Yes we are talking about notifications ( every time someone does something on Facebook for example , you end up with an email ) that end up in your inbox from your social media accounts.
Edward Snowden ended up with 47gb of email notifications after he recently joined Twitter
So how do you stop this happening ?
Open settings , look for Notifications in the left hand column and open
From here you can adjust what notifications you will get from email / mobile , my advise is to turn most off as you can just go to Facebook when you want to see whats happening.
Facebook have advice on notifications at this link : Facebook Notifications
To adjust your Twitter notifications , go into your settings and then look for Email Notifications.