From XMission Wiki
- Press the home button, tap on the Settings icon and then tap on the Fetch New Data option.
- In this screen you can specify how often you want your IPhone to check for new emails and turn on or off Push data (for Zimbra hosted accounts). A longer fetch schedule will save battery life. You can also select Manually if you only want the device to check email when you tell it to.
Tap on the Settings chevron to save your changes.