How can I avoid receiving Flipboard emails/notifications
To stop receiving emails from Flipboard, simply unsubscribe from their email list. You can usually find an unsubscribe link at the bottom of the email. 

If you can't find the link, use this page to unsubscribe.

To stop receiving notifications from the app, go to your phone settings -> application Manager -> Flipboard -> notifications, and switch "allow notifications" to "off"