Go into SETTINGS > MAIL,CONTACTS... > FETCH NEW DATA > and unless you need instant notification, set the fetch for hourly or less, to save battery. If you have multiple accounts, select ADVANCE on that page and you can set up each account to fetch when you want it to. Also you can set PUSH on the first page. If you need every thing quickly, then just turn PUSH on, but that is a big hit on the battery life, because it's constantly checking for mail all the time and using up your data plan. Could get expensive real quick.
