Email delivery failures and other Yahoo mail sending issues
Does your email is getting failed and not you are facing delivery failure issue in your Yahoo mail account? If yes, then it means that the server reputation is not good. Or it can also be possible that the recipient has blocked your email address. Apart from this if you have linked your account from a third party email client, then it might be possible that there is some issue with account settings. So, you need to figure out an issue and enjoy the exceptional email account services.
More detail: https://www.supportforhelp.com/contact-yahoo-number.html