failure Sending email on minimac

Please read If you can’t send or receive email on your Mac - Apple Support.

For reasons unknown, sometimes something happens to the email settings. It is necessary to understand that in order for the email app to connect to the email provider's server, an exchange of information takes place. The user ID and password must then be accurately sent to the server within a specified period of time or a disconnect occurs. If there is any difference in what data is transmitted and what is being looked for, the connection will not occur. Therefore, something is not being sent correctly. You can open the email app and very carefully check  what you have entered for the user ID and password and correct it. Or you can delete the account from your email app and create a new one. That often solves the problem. If you choose to delete the account, be sure to first save any email messages to a local folder or they will be lost.