I have a Samsung Galaxy S4 mini running Android 4.2.2 and my network provider is O2.

When I’m connected to a WiFi network the phone syncs to my mail without any issues. However, when I’m outside a WiFi zone and have to use the O2 3G network, the mail won’t sync at all. Not even when I manually press the sync button. I had a similar issue with my previous phone which was a Sony. Any ideas how I can overcome this??  The App is pretty useless if I can only access mail whilst on WiFi.