If you get a lot of incoming e-mail, personal or business related, it can clog up your inbox. Make things more manageable by limiting the number of messages displayed on the iPhone and/or the number of lines previewed for each message.
To set the number of messages displayed in the inbox, go to Settings >Mail, Contacts, Calendars >Show. Then select 25, 50, 75, 100, or 200.
To set the number of lines displayed, go to Settings >Mail, Contacts, Calendars >Preview. Then choose from none to 5 lines.
You’ll have to experiment with these settings to see what works best for you.