I’ve been working on the iPhone, since my old HTC died. One thing I found annoying about the iPhone was the inability to sync more than a few days email. I searched and found what I needed.
First, how to sync the iPhone to Exchange – http://blog.powerbiz.net.au/sbs-2008/configuring-the-iphone-for-exchange-sync/
To sync more than the default of 3 days, Open up Settings,
Mail, Contacts, Calendars, [your exchange account],
Mail Days to Sync.
Select the desired setting.