problem with older computer using macmail and smtp - says it's offline

SMTP server problem using mac mail on an older imac (27 inch, late 2013). Running Catalina-- that's as far as it goes. My email provider is earthlink. Yesterday changed my password. On my lap top the change is fine; also fine in web mail. On this iMac- it says smtp is offline. Can't send email. Anyone know how I can fix this? (I know- get a new iMac but this one is usually fine for what I need it for). (Waiting for the 32")

Is it something in the settings that is causing this?