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In the Fetch New Data part of settings, select how often you want your mail to be checked for. You can do 15, 30, or 60 minute intervals.
 
Thanks!

What exactly does push do? I never understood it, though I've been explained about many times.
 
Push basically sends the email to your iphone on the second that you receive it. Same goes for contact/calendar edits. You have to be using a service running exchange, which few free services use.
 
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