It seems to be a problem if you save lots of emails on your server. I tend to delete most of them from the mailbox and handheld. Then they don't all push again to the device. Remember, with Gmail all the mails you delete are kept in the trash folder for quite some time if you need to get them back.
Mine was sending the smae 100 emails atleast 4-5 times a day that was before i returned the device for faulty charging and once i got the new 8830 it never did the same thing.. thank god.
It can also be a service book issue. You can delete all the service books then resend them to the device. That could be what fixed your issue when you exchanged the device.