Mail keeps asking for password for sbcglobal mail account
I've been using a sbcglobal.net account on my iMac and other devices for years. In the last two weeks, it has asked me to re-enter the password. I was able to do it the first time but I can't get it to work today. I logged onto Yahoo mail with the username@sbcglobal.net and password and saw the emails I expected. But when I go to Systems -> Internet Accounts >- username@sbcglobal.net and enter the username, I am then presented with a screen the requests the username and password. I enter both and then I keep getting directed to a blank screen the displays "Unknown Destination."
This is an account I use for newspaper columns, etc. so it is not critical. I deleted the account from Internet Accounts and then tried to add it again as a Yahoo Account. I get the same prompts, i.e. username, then a screen asking for username and password. But this time all I get is a blank white screen with an option to cancel. I have another sbcglobal.net account under a different username on my iMac and it works just fine. I'm up to date on the latest iMac (2019) system software updates, i.e. 11.2.3 (20D91).
iMac Line (2012 and Later)