If you want to prolong your iPhone's battery life, disable Push email and enable Fetch instead. This means your phone won't constantly poll the server to find out if there's new email, but will check every 15, 30 or 60 minutes depending on which option you choose. For better battery life, choose the longest interval you can live with.

To see these options, tap Fetch New Data from the main Mail, Contacts, Calendars menu.

If your email provider isn't in the list when you tap Add account... then you'll need to choose the 'Other' option.

Enter your email address, password and a description for the account and tap Next. Select between IMAP and POP at the top of the screen and enter the details for the Incoming Mail Server.