If you want to know how to block an email address on Yahoo mail, then proceed to Yahoo mail on a web browser and then tap the cog icon in the top-right corner, which is beneath the home button. Choose more settings in the drop-down menu at the bottom. In the left-side menu, tap to security and privacy tab. Click on add next to the blocked address. Enter the email address you want to stop and then tap to save. After performing these steps, you are all set to see the newly blocked email address.