This tip no longer works for devices running iOS 7 or later.
By default, you will see a certain number of messages when you open your Mail app. Your device will show you the sender, the subject line, and a two-line preview of the e-mail. To change the number of messages shown:
- Open Settings>Mail, Contacts, Calendars.
- Tap on Show.
- Tap on the number of messages you want to show in your inbox.
You have the option of displaying 25 to 200 recent messages at a time in your inbox.