1. Checking email options;
2. Deleting all service books and resending;
3. Deleting email accounts and re-adding them; and
4. Rebooting.
None of the above works. I am O2 UK on the 8310 Curve, and it used to work on my Curve. I'm wondering if downgrading will solve it, but worried it may not be an OS issue.
You normally do need to delete the vendor.xml file each and every time you install a new OS to your PC which is not released by your device-branded carrier. I am surprised if you did not, or else did you actually upgrade?