In the iCloud preferences, Mail was already marked. When I returned to the Mail app, Accounts preferences, the incoming mail server had changed to mail.example.com, dimmed, and I was not allowed to type anything into that field.
Given that I have already set up iCloud and use it for data synching with an iPad and iPod Touch, how can I start the email setup over again. or should I?
I would seem that if i delete the iCloud account in Apple Mail, and the try agan to add it, i will just be repeating what i have already found to be impossible.
Well, for the moment, all is well, but I am not sure why. I un-marked Mail in iCloud prefs, and when I marked it again, the panel said it had to be done in my mail program. (Why it's this way sometimes, and the other way sometimes remains a mystery.)
Then I went to Mail and set up an iCloud account, changing as little as possible. For example, before, I had used XYZ@icloud.com as my email addrss, but this time, I used XYZ@me.com, just because some little tea leaves said that was better. And i eschewed changing the deafult mailbox behaviors, whereas before, I had made it keep trash forever.
So this time it worked!
In the past, when I have had an iCloud account set up in Mail, the connection to the outgoing iCloud mail server would fail for no known reason, as confirmed by Connection Doctor. But now, (AS LONG AS I TOUCH NOTHING), it seems to be OK.
One additional mystery: though my iCloud account shows that it uses the iCloud server for outgoing mail, none of my other accounts can use it for outgoing mail, because it doesn't show up in the list of servers. Is that docmented or explained anywhere?
I will keep this inquiry open for a few days, in case something else goes South.