Q: mac os 10.8.3 Mail

Activity shows attempt to connect but connection is not made, alert symbol still shows at inbox. Connection Doctor says "Could not connect to this iCloud IMAP server. Then says to check network connections and account info. Have not changed account info, all seems to be as it should be.

Reading further in the Connection Doctor says to check that the server supports SSL, and if it doesn't to uncheck Use SSL box. Did this and now mail is working. Thanks for leading me to the Connection Doctor, though I still don't know what SSL is and more importantly, how the settings got changed when I updated the OS. All's well that ends well.

Mail has re-checked the SSL button and the warning sign is back at the inbox. Problem is NOT solved.

What finally worked was following the iCloud - Mail Troubleshooting and setting the port to 993 and enabling SSL. So far so good and thanks for the link Troubleshooting.