If Yahoo mail is not working for you and your Yahoo mail is not sending all emails, don't worry, it happens due to some technical problem. You can troubleshoot your problem by implementing all these steps -
1. Check Yahoo server should work properly.
2. Check that your Yahoo Mail is properly connected to the Internet.
3. Install the latest version of the Yahoo app
4. If you are using Yahoo with an email client, make sure you have
Configure the correct POP / IMAP settings for your Yahoo Mail.
5. Check the email address you are entering to send the email.
After doing all these steps you can send email to your Yahoo account.
For more info - https://getassist.net/