Conserve your mobile data plan by setting guidelines on what items to download on your device and when:
1.Tap the Nav icon at the top left corner of the Nav Bar to display the Navigation Drawer.
2.Tap the Gear icon at the bottom of the Navigation Drawer to bring up Settings.
3. Tap Mail.
4. Under the Data Usage section, tap Auto-download attachments.
5. Tap "When using Wi-Fi". Select your preference.
6. Tap "When using mobile data". Select your preference.
7. Tap "When roaming". Select your preference.