iPhone and iPod touch: How to configure Exchange Mail settings to increase or reduce the amount of emails displayed on the device
Summary
When Microsoft Exchange mail is configured on iPhone or iPod touch, the default setting for "Mail days to sync" is set to 3 days.

Products Affected
iPhone, iPod touch, iPhone 3G
To increase or decrease the amount of email messages displayed in your Microsoft Exchange mail accounts (Inbox, personal folders, Sent, etc.) change the "Mail days to sync" for the account.
From the Home screen tap Settings > Mail, Contacts, Calendars. Select your Microsoft Exchange account and then tap Mail days to sync and select the number of days (No Limit, 1 day, 3 days, 1 week, 2 weeks, or 1 month)
Additional Information
Note that the Mail setting to set the number of messages on the iPhone (tap Settings > Mail, Contacts, Calendars > Show) does not apply when using a Microsoft Exchange account.
Important: Information about products not manufactured by Apple is provided for information purposes only, and does not constitute Apple's recommendation or endorsement. Please contact the vendor for additional information.