The "This message has not been downloaded from the server" error on iOS typically occurs when the email app is unable to retrieve a specific email from the server. This can be caused by a number of factors, including a poor internet connection, a problem with the email server, or an issue with the email app itself.
Here are some steps you can take to fix the error:
Check your internet connection: Make sure your device is connected to a stable internet connection. If you're on cellular data, try switching to Wi-Fi.
Refresh the email account: Try refreshing the email account by pulling down on the inbox screen to manually check for new messages.
Check server status: Sometimes the issue may be with the email server. Check the status of the email server and see if it is down or experiencing issues.
Restart the device: Restarting your device can help clear up any temporary issues that may be causing the error.
Delete the problematic email: If the error message is only showing for a specific email, try deleting the email from the server.
Re-add the email account: Sometimes simply re-adding the email account to the device can fix the issue.
Update the iOS: Make sure your iOS version is up-to-date.
If the problem persists, it might be a good idea to contact the email server's technical support for further assistance.