HERE IS A SOLUTION! I was having the same issue. The LED would blink for text messages but not for emails. I also had the notification sound set to "Silent" for emails. Following your lead, I...
See more...
HERE IS A SOLUTION! I was having the same issue. The LED would blink for text messages but not for emails. I also had the notification sound set to "Silent" for emails. Following your lead, I confirmed that selecting a sound to be played upon email arrivals also activated the LED for emails. The default sound on my device is set to "Silent." If you select "Default Sound" as the email notification sound, then the LED will blink for unopened emails! If you set it for "Silent," then it will not blink. It's a bit round about but it works. Having my default sound set to silent is no issue for me because I select the sound I want for each app that I want to provide an audible notification.