I haven't had email since May

My notes, no isea why Mail providers don't notify their own users...

Mac's Mail App is not as modern as iOS's Mail app, Many eMail providers now require a separate App Password different from your eMail password…

Yahoo has gone to this too...

https://help.yahoo.com/kb/access-yahoo-mail-third-party-apps-sln15241.html

Cox for Apple Mail…

https://forums.cox.com/discussions/internet/using-yahoo-email-in-mac-os-mail-app/151730

Yahoo cure, thanks to tekkaman65535…

yahoo mail failed to authenticate - Apple Community

yahoo mail failed to authenticate - Apple Community

tekkaman65535 Posted on Aug 9, 2023 10:20 AM

I found a solution for this.

• Delete your Yahoo! account from Internet Accounts.
• Go to your Yahoo! account in your browser.
• Click on your account on the top right.
• Click Security.
• Click Generate and manage app passwords.
• Enter "Mail" when prompted for an App.
• Copy the password Yahoo creates.
• On your Mac, go to System Preferences > Internet Accounts.
• Instead of clicking Yahoo!, click Add Other Account.
• Click @ Mail account.
• Enter your Yahoo! email address and paste the app password you just generated on the Yahoo! website.

This worked for me and I now have my Yahoo! emails actively coming into the Mail app on my Mac.

yahoo mail failed to authenticate - Apple Community

Yahoo App password…

Generate and manage third-party app passwords

Some older, third-party email apps (that do not use our Yahoo branded sign in page) require you to enter a single password for login credentials. To access your Yahoo Mail account on these apps, you'll need to generate and use an app password. An app password is a long, randomly generated code that gives a non-Yahoo app permission to access your Yahoo account. You’ll only need to provide this code once to sign in to your third-party email app.

https://help.yahoo.com/kb/access-yahoo-mail-third-party-apps-sln15241.html

Most likely biggest factor is using Other in Mail setup, then using a Browser that doesn’t have Yahoo PW stored init to get the App PW.

Changed Yahoo password, yahoo stopped sen… - Apple Community

Tesserax's reply jogged my memory. As I recall AT&T recently transitioned their email services to Yahoo. If that's the case I think your best avenue for support would be to ask them, here: https://www.att.com/support/email-support

Edit to add: That memory jogged more memory. Even though this solution is for Cox email and not AT&T, the solution does not involve Cox at all. It describes the Mail settings that need to be configured for Yahoo Mail:

https://forums.cox.com/discussions/internet/using-yahoo-email-in-mac-os-mail-app/151730

Scroll down to the reply Marked as Solution. Presumably, those same settings will apply to your email account. Try it, but if all else fails you may need to contact AT&T and I wouldn't wish that upon anyone.

First please review If you can’t send or receive email on Mac - Apple Support. Exhaust all those steps. Exclude none of them. Report the results of each step.

I don't understand what Yahoo has to do with AT&T but perhaps that's a question we can discuss next.

If you don't back up your Mac, that means you have no concern about spontaneously, permanently and irretrievably losing everything it contains. Some people don't, and if that describes your situation then it's ok. That concern is unrelated to email problems though. Back up your Mac as a matter of course. To learn how to use Time Machine please read Back up your files with Time Machine on Mac - Apple Support.

Just to add a bit to what John Galt has provided you ...

Do you have a Yahoo email account? Is this account being provided to you by AT&T?

POP & IMAP are two different types of incoming mail services. Although they both provide you a means to receive emails, they do so via a different process. You normally would only have your email account set up for one or the other ... not both.

Do have two-factor authentication (2FA) configured on your Yahoo email account? If so, then the "warning" you are seeing may be related to when you try accessing your Yahoo account via a dedicated eMail client, like Apple Mail. 2FA is becoming the standard for user accounts for security reasons. This issue may not have anything to do with the version of macOS, but your eMail account.