This video is only applicable to those who have NOT updated their iPhone/iPad to iOS 7 or 7.1 Please see additional videos for iOS 7 and higher.
If you use folders to store e-mail, and you want to have instant access to e-mail stored in certain folders, you will want to take a look at your “Mail Folders to Push” settings. This process is the same on the iPad and iPhone.

For example, if you use Outlook and you move an e-mail into a folder, if the folder is set to “Push”, the e-mail will show up in that folder on your iPad immediately. If you do not “Push” a folder, you will still be able to see the e-mail after you open the folder on your iPad and let the folder download. Depending on how much mail you keep in your inbox and folders will determine how much memory is used on your iPad for e-mail. If you “Push” a lot of folders it will deplete your battery a bit faster.