You can follow the steps mentioned below in order to block certain email addresses to stop receiving emails from them:
1. Sign in to your Yahoo account and go to “mail options”
2. Go to “blocked addresses” option
3. Now go to “add an address” box and type the email address you want to block
4. Now click the “Block” button that will add the email address to the blocked list
5 .You can add as many email addresses as you have to block.
So these are the 5 steps to block email in yahoo account if still getting any issue so you can contact Yahoo support service by an official source.