Hello Illaass:
Thank you, I think you answered my questions. I can access the same accounts from my iPhone and Yahoo account. I checked my email this morning on my mac mini desktop and the issue corrected itself, mail downloaded.
Now, what I found strange is that I have another account that has duplicated itself on my apple mail. One account has the IMAP address that I tried to change the incoming pop server name on. The new duplicate mailbox that appeared is set to the IMAP server name. What would cause that to happen? In summary, when I log into preferences I see two icons for the same mailbox that display the mailbox name and below it also displays Yahoo! IMAP. When i look at the settings, one is set to the att pop name that i had changed it to and the new mailbox that appeared shows the imap yahoo name.
Hope you can help.