iPhone Life magazine

Limit e-mail to reduce e-mail 
 overload and improve battery life

You can further reduce the drain on the battery and reduce e-mail overload by limiting the amount of e-mail you download to your iPhone. Immediately below the Auto-Check setting on the Home >Settings >Mail screen is the Show setting. You can set this to display a specific number of the most recent messages: as low as 25 and as many as 200. If you want to see additional messages, tap on the Download More button in the Mail program.