How can I fix error message, "Connections to the server “p71-imap.mail.me.com” on the default ports timed out."

iCloud mail problems on iMac!

2 days ago I started to get the following Error Message on Mac Mail on my iMac: "There may be a problem with the mail server or network. Verify the settings for account “iCloud” or try again. The server returned the error: Connections to the server “p71-imap.mail.me.com” on the default ports timed out."

I have already followed all of the help guidance I can locate for this problem and have been going round the same help pages in circles! I should add that I can still get iCloud mail on Mail app on all my other devices, MacBook Pro, iPad and iPhone.