I see my emails and can read the 3-line tags in my inbox, but when I go to open the message to read the full text, it is just blank - regardless of the size, number of recipients etc.
What causes this kind of behavior and how can I solve this issue?
When I had this problem it was due to a network issue. Make sure that you are able to surf the web in "accurate" speed. If websites will not load, restart your phone.
If websites are loaded as fast as ever, restart your phone nevertheless (press the key in the upper right corner for a few seconds). I would also suggest to completely close the Mail.app before (doubletab on the home button, press and hold the mail icon until it starts wobbling, click on the red X on the corner when it appears).
I had this problem with an older iphone and ios 6. the universal way of resetting your phone with the sleep and home page button held down for 10 secs did the trick. See below link in the apple support page. https://discussions.apple.com/thread/3916566