Step 1:Check if there is any update for your mail app. If yes, then upgrade it and check if the Email error has been resolved.
Step 2:Restart your device in the next step to solve this problem.
Step 3:Also, check if you are connected to the Internet properly. If you have a low speed Internet connection at your place, then the syncing process will take a longer time.
Step 4:Disable the Airplane Mode on your device if you have turned it on.
Step 5:Navigate to Account Settings and check if the box near the Sync Gmail option is checked.
Step 6:Check if there is enough space for the mail to sync. Free up space if enough memory is not available.
Step 7:Clear cache data from your device to rectify this error.
Step 8:Get in touch with the technical experts if you are unable to sort out the error for Email Not Syncing.