The mailbox may have some emails with an excessively long subject line that are not supported by Windows Phone 8. Once you have removed the suspect mail item (i.e. cleaned the mailbox or move the suspect mail to a folder that phone does not sync) the error will cease.
- What happens to my map if I restore my Windows Phone to factory settings (hard reset)?
- Can I move or save apps to my memory card on my Lumia phone?
- Does my Lumia support “Hey Cortana” Voice Activation?
- I forgot my Nokia account password for my Lumia. How do I recover my account?
- How to unlock the lock screen on my Lumia when Narrator is turned on?