When the Push option is turned on, and if your e-mail service provider supports Push, information updates are sent to your iOS device as your provider receives them. (MobileMe, Microsoft Exchange, Yahoo! Mail, and some others support Push.) However, leaving Push on all the time consumes battery power. Unless you have up-to-the-minute messaging needs, you should turn Push off and use the Fetch option, which checks for messages periodically. Here's how you do it:
- Open Settings>Mail, Contacts, Calendar.
- Tap on Fetch New Data.
- If Push is on, turn it off.
- In the Fetch section of the screen, select how often you want your device to check for e-mail (Options: Every 15 Minutes, 30 Minutes, Hourly, or Manually).