Hi @c c ,
Welcome to our forum.
I had no problem with @Stuff .com and @Karima ben .com email accounts
Considering you could configure other accounts on your Outlook 2019, there may be no issue on your outlook client, and the issue may be more related to your account itself or the configuration on Outlook.
As I know, if Outlook won’t accept your password and you know you’re using the password for your Yahoo! account, your email account likely requires additional security--two-factor authentication and application password, which may cause your issue.
In this case, it's suggested to go to the Yahoo website from your browser, turn on the two-factor authentication and configure your account with application password in Outlook to check if the issue has any difference. For more information, please refer to this article : Can't add an Yahoo! email account to Outlook
If the issue still exists, in order to further analyze your issue, it's also suggested to log in your account to other outlook client to check if your yahoo account could work normally there.
If your issue has any update, please feel free to post back.
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