Mail app can't get a connection

Mac Mail app for my iCloud Mail account is coming up with black ! triangles, and indicates "Connections to host p02-imap.mail.me.com on the default ports failed."

in iCloud.com via Safari, I see all my messages.

High Sierra 10.13 was installed from App Store on 10/8/17 and Mail has worked fine until today.

I've visited Mail prefs and accounts, and the settings look right, although I'm not confident with the complexities of email settings.

I can't find a "community" that has "Mail" in its title. Sorry if I'm sending this to the wrong place.

Any help appreciated.