Why Yahoo email authentication fails on my iMac

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

https://discussions.apple.com/thread/254879377?answerId=259375262022#259375262022

There are a few reasons why your Yahoo email might not be linking to your iMac anymore, even though it worked before. Here are some easy fixes to try:

Check Credentials: Make sure you're entering the correct Yahoo email address and password. Sometimes a typo can cause the connection to fail.

Remove and Re-add Account: Sometimes removing the account and re-adding it can refresh the connection.Here's how to do it:

• • Open System Preferences.
  • Click on Mail.
  • Select your Yahoo email account from the list on the left.
  • Click the minus sign (-) button below the list to remove the account.
  • Now, click the plus sign (+) button and choose Yahoo from the list.
  • Enter your Yahoo email address and password.

1. Enable Two-factor Authentication (2FA): If you haven't already, enable 2FA for your Yahoo account. This adds an extra layer of security and might be required for some less secure connections. You can enable 2FA from your Yahoo account settings.
2. Check Yahoo Settings: Yahoo might have recently changed some settings that affect how external apps connect to their email service. Check your Yahoo account settings for any options related to POP/IMAP access or app passwords. You might need to generate an app password specifically for your iMac Mail app.

If none of these easy fixes work, there could be a temporary issue with Yahoo's email service. You can check online forums or their official website for any reported issues.