iMac, iCloud sync question

Did you configure Mail manually by any chance.

Try removing the account from Mail and then turning Mail on in the iCloud settings. It should configure it for you.

You shouldn't if it's an iCloud account, deleting the account should only delete the data from your Mac it shouldn't delete it from the account, so when you add it back, your Mail should re-appear.

You really shouldn't need to but if you have any doubts you can copy the mail you alrerady have to 'On My Mac' folders, before doing anything.

I need to remove the account from mail and then add the account again?

Instead of deleting the mail account, could I just uncheck enable this account (in Mail account preferences)?

Possibly, I'm not sure, you could try it.

And lastly, should I even be concerned that "Mail" doesn't stay checked in "iCloud preferences" and "Mail, Contacts & Calendars" , as long Mail is syncing perfectly fine between iMac, iPad, & iPhone?

Possibly not. Does notes stay checked.

That's a bit strange, but maybe if it's all working fine, the best thing to do might be to leave it alone.