This article explains how to block unwanted emails from up to 500 addresses in Yahoo Mail. The instructions in this article apply to the web versions of Yahoo Mail.
How to Block Junk Emails on Yahoo! Mail [Tutorial]
To block email messages in Yahoo Mail, follow these steps:
Go to Yahoo Mail in a web browser, sign in to your account, and select the Settings gear icon in the upper-right corner of the window.
Select More settings at the bottom of the Settings pane.