When using Yahoo
Yahoo Mail can help you out with a handy feature that lets you list email addresses that you would like blocked from your Yahoo! Mail account. When emails arrive from addresses that you’ve blocked, Yahoo! Mail automatically delete them.
1. In the upper-right corner of your Yahoo! Mail page, click the Options link, then select Mail Options from the menu.
The Mail Options page opens.
2. Under the Spam column, click the Block Addresses link.
The Blocked Addresses page opens.
3. In the Add Block area, type the email address you wish to block, then click the Add Block button.
Tip: To block email messages from an entire domain (for example, baddomain.com), type the domain in this box.
The address is added to your list of blocked addresses.