Here are the steps that you have to follow while you try to block email on Yahoo Using a PC.
If you don't have an email from the sender, you can still block them by going to your Yahoo Mail settings.
Click on the gear icon in the upper-right corner of the Yahoo Mail interface to open the Settings menu.
Select "More Settings" at the bottom of the menu.
In the left sidebar, click on "Security and Privacy."
Under the "Blocked Addresses" section, enter the email address you want to block and click the "+" button.
Then follow online instruction and block it easily.
If you don't have an email from the sender, you can still block them by going to your Yahoo Mail settings.
Click on the gear icon in the upper-right corner of the Yahoo Mail interface to open the Settings menu.
Select "More Settings" at the bottom of the menu.
In the left sidebar, click on "Security and Privacy."
Under the "Blocked Addresses" section, enter the email address you want to block and click the "+" button.
Then follow online instruction and block it easily.