Unable to send mail. Outgoing Mail Account: iCloud (Offline)

This seems to be an ongoing issue for many years.

16" M1 MacBook Pro 2021, macOS 12.3.1, Mail 16.0

I am able to receive mail but not send. My account is online (green dot in the Mail : Accounts : Account Information tab) but in Server Settings I see "iCloud (Offline)"

I was able to get things working briefly by following some advice I found online:

1. Uncheck "Enable this account"
2. Restart
3. Check "Enable this account"

This worked for a while but I now am unable to send emails again.

Does anyone have any suggestions?