By default Office 365 sends you email notifications for all sorts of things: when someone follows you, when someone replies to your discussion posts, when someone mentions you, etc.
If you are regularly checking your Newsfeed (and I suggest you should!) you probably do not want to also receive emails for all these events. It is simple to turn off these notifications (if you know where to look).
- Click on your name at the top of any Office 365 page, and click About Me.
- Click edit your profile on the top right of the page.
- Click the ellipsis (…) after Details and choose Newsfeed Settings.
- Now you can choose what you are notified about as well as what activities you want to share with other users: