Imcoming eMail Server Doesn't Recognize username
For the last week or so the incoming email server will, on occasion, not recognize my username/password. The outgoing email server is fine, as I can send mail. This happens when the account is set up either as IMAP or POP. The inbound and outbound server names are correct for the type of account, and the same username/password is used for incoming and outgoing mail servers, of course. Later in the day or the next day things work fine again. When this happens it happens on the 3 devices I normally use. They are an iPhone 8 set up as POP, an older Windows 10 laptop set up as IMAP and using Windows Live Mail as the mail client, and a brand-new Win 10 laptop set up as POP and using Outlook 2016 as the mail client. Yes, I can go to ATT.net and log in to read my mail, that works ok, but I hate reading my mail that way. My wife's email account doesn't have this problem, and sends/receives fine on all 3 devices when my incoming mail server won't connect. Except for her username/password her account is using the same server settings as mine.
I've tried everything I can think of, including spending more than 3 hours on the phone with ATT tech support. Does anyone have ANY idea what the problem might be?