Unable to send emails from Hotmail on older iMac

I'm trying to send emails from my Hotmail which stopped receiving new mail 9-28 and it reads "This message could not be sent because your account does not have a preferred outgoing mail server. Select an outgoing mail server from the list below."

But no list shows up. I tried to register it on the exchange. Help, what am I doing wrong? Thanks! New to Apple and I have an older desktop iMac

[Re-Titled by Moderator]