The following steps will detail how to fix the Cox email not sending on Windows 10 email issue as it is the main reason you encounter the issue:
Be sure the server settings given below perfectly match the email account you are using with Cox.
Poor network connectivity can sometimes cause issues. Make sure your internet connection is strong.
You should also check your credentials, such as your username and password. If they are wrong, you have to enter the correct details.
Make sure that IMAP is the account type.
Make sure that your TLS or SSL settings are enabled.