1. Check your device settings to ensure that the email account is properly configured.
2. Check the network connection of the device and the email server to make sure that it is stable and secure.
3. Clear the app data or delete and reinstall the app on your device.
4. Check if the email account is synced across other devices or not.
5. Try signing out and signing back in to activate the sync process.
6. Check if any third-party applications are blocking the sync process.