Email on iPad not showing after some days
If you have an Exchange account or even a Gmail account configured as an Exchange account, there is an option in the email settings for Exchange to only sync up to a certain number of days worth of email. By default, it it set to 3 days. You can change this by going to Settings > Mail, Contacts &amp; Calendars, tap on the email account in question and change the "Mail Days to Sync" option from 3 days to whatever you desire (I use No Limit).

Hope this helps.