I'm back........the fix caused a new problem.
To summarize the original problem.
Suddenly Air 2's Yahoo mail which was setup thru Settings was totally empty. Update said Updated yesterday. All "added" mailboxes were gone. Attempts to again setup Yahoo mail was unsuccessful.
Solution
Note my email address ends in "@sbcglobal.net". Used Chat on my PC to contact Apple. Rep had me create a new email account in Settings using Other account. Upon filling in the fields Sbcglobal appeared as the email account AND all remaining fields were populated.
Air 2 Sbcglobal email account sends and receives without error but all original added Mailboxes were not brought over. Additionally, when I attempt to creat a new mailbox the message "Unable to Create Mailbox" "The mailbox couldn't be created on the server."
Two requests from you.
1. Solution to re-creating original Yahoo account.
2. Solution to creating new mail boxes for Sbcglobal email account.