Did you try to delete your e-mail account from the device and then add it back? You should also be able to go into settings>application>application manager>all and try and find the e-mail you use and delete the cache and data.
Yeah, it won't hurt to delete them from your device. You'll just need to know your e-mail address, and your password to add them back. You may need to adjust your sync settings etc. It won't delete your e-mails.