Hello and welcome to the forum. The display should be the one showing the highest percentage (at least that's how it is with my EVO phones), but It's not unusual for a different device to show something else. You really shouldn't be using a "task killer"... because they can cause more complications than anything else. What you should do is, Uninstall the task killer - and clear the data from the mail application. Proceed with setting up your email account(s) and check to see if you're still having the same problem. If you have any other problems or concerns you can post them in your device's home-forum.
Note: If an application other than the preinstalled ones are showing a higher percent - then you might want to Uninstall that application.