I guess you are another than needs a "secure mail key" https://www.att.com/esupport/article.html#!/email-support/KM1240462

I think you are on the right track, but I have no idea how to set up my account to use OAuth or a "secure mail key". I've poked all the buttons I see in Tool>Account Settings>Server Settings. No joy.

I'm using:

inbound.att.net Port 995 Security SSL/TSL Authenication Normal Password (OAuth is not a choice)

I've tried: imap.att.net Port 993 and 995 Authentication Entrypted and Normal

No luck.

Any specific suggestions?

fropm the ATT web site

Create a secure mail key Learn how to create a secure mail key from your mobile device, tablet, or computer. Have your User ID and password ready to sign in to myAT&T.

• Go to Profile > Sign-in info.
• Select the email account that you want to get a secure mail key for. (You’ll find a drop-down menu at the top if you have multiple accounts.)
• Scroll to Secure mail key and select Manage secure mail key.
• If you have more than one email address, select the one you want to use.
• Select Add secure mail key.
• Enter a nickname for the secure mail key to make it easier to recognize.
• Select Create secure mail key.
• Select Copy secure mail key to clipboard. (Jot down your secure mail key, so you have it handy if you have to update an email app on several devices.)

For security purposes, the secure mail key only shows until you select OK. If you lose or forget the secure mail key, you can create new secure mail keys as needed.

• Select OK.
• Go to your preferred email app and replace the existing password with your secure mail key. (For an IMAP account, delete the existing password for both the IMAP and SMTP servers and replace them with your secure mail key.)