Short Answer 
Begin by ensuring your device has a stable internet connection; switch to Wi-Fi if necessary. Then, refresh your email account and restart your device to eliminate minor issues. If problems persist, check the email server status and consider re-adding your email account.
Step 1: Check Your Internet Connection
Begin by ensuring that your device is connected to a stable internet connection. If you are using cellular data, switch to a reliable Wi-Fi network to see if that resolves the issue. A poor connection often hampers the email app’s ability to retrieve messages from the server, leading to the error message.
Step 2: Refresh and Restart
Next, refresh your email account to check for new messages. You can do this by pulling down on the inbox screen. Additionally, try restarting your device, as this can eliminate any temporary glitches that could be affecting the app’s performance. This simple step often resolves minor issues.
Step 3: Troubleshoot Server and Account Issues
If the error persists, assess the status of the email server to determine if there are ongoing problems. You may also consider deleting the problematic email if it appears to be an isolated issue. Finally, try removing and then re-adding the email account to refresh its settings. This can often correct deeper configuration problems.