Here are the steps which you can take to fix the Yahoo Mail error code 475 issue.
1. First of all sign out from your Yahoo mail account and then sign in again.
2. Wait for sometime and then try to send email to a single recipient
3. If you are not able to send a lot of email from your Yahoo account, then you should need to reset your Yahoo password.
4. If the error is still there then can visit the Yahoo help page for more help.